Editing IPCC:AR6/SROCC/Chapter-5 (section)

==== 5.2.3.1 The Epipelagic Ocean ====

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This section synthesises new evidence since AR5 to assess observed changes in relation to the effects of and the interactions between multiple climate and non-climate hazards, and to project future risks of impacts from these hazards on the epipelagic organisms, communities and food web interactions, and their scope and limitation to adapt.

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===== 5.2.3.1.1 Detection and attribution of biological changes in the epipelagic ocean Temperature-driven shifts in distribution and phenology =====

WGII AR5 concluded that the vulnerability of most organisms to warming is set by their physiology, which defines their limited temperature ranges and thermal sensitivity (Pörtner et al., 2014 <sup>[[#fn:r385|385]]</sup> ). Although different hypotheses have been proposed since AR5 to explain the mechanism linking temperature sensitivity of marine organisms and their physiological tolerances (Schulte, 2015 <sup>[[#fn:r386|386]]</sup> ; Pörtner et al., 2017 <sup>[[#fn:r387|387]]</sup> ; Somero et al., 2017 <sup>[[#fn:r388|388]]</sup> ), evidence from physiological experiments and observations from paleo- and contemporary periods continue to support the conclusion from AR5 on the impacts of temperature change beyond thermal tolerance ranges on biological functions such as metabolism, growth and reproduction (Payne et al., 2016 <sup>[[#fn:r389|389]]</sup> ; Pörtner and Gutt, 2016 <sup>[[#fn:r390|390]]</sup> ; Gunderson et al., 2017 <sup>[[#fn:r391|391]]</sup> ), contributing to changes in biogeography and community structure (Beaugrand et al., 2015 <sup>[[#fn:r392|392]]</sup> ; Stuart-Smith et al., 2015 <sup>[[#fn:r393|393]]</sup> ) ( ''high agreement, high confidence'' ). Comparison of biota across land and ocean suggests that marine species are generally inhabiting environment that is closer to their upper temperature limits, explaining the substantially higher rate of local extirpation related to warming relative to those on land (Pinsky et al., 2019 <sup>[[#fn:r394|394]]</sup> ). Hypoxia and acidification can also limit the temperature ranges of organisms and exacerbate their sensitivity to warming (Mackenzie et al., 2014 <sup>[[#fn:r395|395]]</sup> ; Rosas-Navarro et al., 2016 <sup>[[#fn:r396|396]]</sup> ; Pörtner et al., 2017 <sup>[[#fn:r397|397]]</sup> ), although interactions vary strongly between species and biological processes (Gobler and Baumann, 2016 <sup>[[#fn:r398|398]]</sup> ; Lefevre, 2016 <sup>[[#fn:r399|399]]</sup> ).

Shifts in distribution of marine species from phytoplankton to marine mammals continued to be observed since AR5 across all ocean regions (Poloczanska et al., 2016 <sup>[[#fn:r400|400]]</sup> ). Recent evidence continues to support that a large proportion of records of observed range shifts in the epipelagic ecosystem (Poloczanska et al., 2016 <sup>[[#fn:r401|401]]</sup> ) are correlated with ocean temperature, with an estimated average shift in distribution (including range centroids, northward and southward boundaries) from these records of 51.5 ± 33.3 km per decade since the 1950s (Figure 5.13). Such rate of shift is significantly faster than those records for organisms in the seafloor; the latter has an average rate of distribution shift of 29.0 ± 15.5 km per decade (44% of the records for seafloor species with range shifts that are consistent with expectation from the observed temperature changes)( ''very likely'' ) (Figure 5.13). Comparison of global seafloor-derived planktonic foraminifera from pre-industrial age with recent (from year 1978) communities show that the recent assemblages differ from their pre-industrial with increasing dominance of warmer or cooler species that are mostly consistent with temperature changes (Jonkers et al., 2019 <sup>[[#fn:r402|402]]</sup> ). Rate of observed responses also varies between and within animal groups among ocean regions, with zooplankton and fishes having faster recorded range shifts (Pinsky et al., 2013 <sup>[[#fn:r403|403]]</sup> ; Asch, 2015 <sup>[[#fn:r404|404]]</sup> ; Jones and Cheung, 2015 <sup>[[#fn:r405|405]]</sup> ; Poloczanska et al., 2016 <sup>[[#fn:r406|406]]</sup> ). For example, analysis of the Continuous Plankton Recorder (CPR) data-series from the north Atlantic in the last decades shows that the range of dinoflagellates tended to closely track the velocity of climate change (the rate of isotherm movement). In contrast, the distribution range of diatoms shifted much more slowly (Chivers et al., 2017 <sup>[[#fn:r407|407]]</sup> ) and its distribution seems to be primary influenced by multi-decadal variability rather than from secular temperature trends. The CPR surveys have also provided evidence that some calanoid copepods are expanding poleward in the Northeast Atlantic, at a rate up to 232 km per decade (Beaugrand, 2009 <sup>[[#fn:r408|408]]</sup> ; Chivers et al., 2017 <sup>[[#fn:r409|409]]</sup> ), although different calanoid species respond differently in the rate and direction of shifts (Philippart et al., 2003 <sup>[[#fn:r410|410]]</sup> ; Edwards and Richardson, 2004 <sup>[[#fn:r411|411]]</sup> ; Asch, 2015 <sup>[[#fn:r412|412]]</sup> ; Crespo et al., 2017 <sup>[[#fn:r413|413]]</sup> ). Overall, the observed changes in biogeography are consistent with expected responses to changes in ocean temperature for the majority of marine biota ( ''high confidence'' ). This is also consistent with theories and experimental evidence that scale from individual organisms’ physiological responses to community level effects ( ''high confidence'' ). Sensitivity of organisms’ biogeography varies between taxonomic groups ( ''high confidence'' ).

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'''Figure 5.13'''

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'''Figure 5.13 | Evidence of climate change responses of marine organisms to changes in ocean conditions under climate change. (a) evidence of interactive effects (including synergistic and antagonistic) of multiple climatic hazards (based on Przeslawski et al. (2015); Lefevre (2016); Section 5.2.2, 5.2.3, 5.2.4, 5.3). ‘Others’ mainly include mammals, seabirds and marine reptiles). The lighter-coloured […]'''
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[[File:c3af71145efc3e74cad05dfb98d228fb IPCC-SROCC-CH_5_13-1.jpg]]

Figure 5.13 | Evidence of climate change responses of marine organisms to changes in ocean conditions under climate change. (a) evidence of interactive effects (including synergistic and antagonistic) of multiple climatic hazards (based on Przeslawski et al. (2015); Lefevre (2016); Section 5.2.2, 5.2.3, 5.2.4, 5.3). ‘Others’ mainly include mammals, seabirds and marine reptiles). The lighter-coloured cell represents insufficient information to draw conclusion; (b–d) observations on changes in latitudinal range and (e–h) phenology (based on Poloczanska et al. 2013). For b–h, each bar represents one record.

The rate and direction of observed range shifts are shaped by the interaction between climatic and non-climatic factors (Poloczanska et al., 2013 <sup>[[#fn:r414|414]]</sup> ; Sydeman et al., 2015 <sup>[[#fn:r415|415]]</sup> ; Poloczanska et al., 2016 <sup>[[#fn:r416|416]]</sup> ), such as local temperature and oxygen gradients in the habitat across depth (Cheung et al., 2013 <sup>[[#fn:r417|417]]</sup> ; Deutsch et al., 2015 <sup>[[#fn:r418|418]]</sup> ), latitude and longitude (Burrows et al., 2014 <sup>[[#fn:r419|419]]</sup> ; Barton et al., 2016 <sup>[[#fn:r420|420]]</sup> ), ocean currents (Sunday et al., 2015 <sup>[[#fn:r421|421]]</sup> ; Barton et al., 2016 <sup>[[#fn:r422|422]]</sup> ; García Molinos et al., 2017 <sup>[[#fn:r423|423]]</sup> ), bathymetry in all or part of their life stages (for organisms living on or close to the seafloor) (Pinsky et al., 2013 <sup>[[#fn:r424|424]]</sup> ; Kleisner et al., 2015 <sup>[[#fn:r425|425]]</sup> ), geographical barriers (Pinsky et al., 2013 <sup>[[#fn:r426|426]]</sup> ; Burrows et al., 2014 <sup>[[#fn:r427|427]]</sup> ), availability of food and critical habitat (Sydeman et al., 2015 <sup>[[#fn:r428|428]]</sup> ), fishing and other non-climatic human impacts (Engelhard et al., 2014 <sup>[[#fn:r429|429]]</sup> ; Hoegh-Guldberg et al., 2014 <sup>[[#fn:r430|430]]</sup> ). Moreover, observed range shifts in respond to climate change in some regions such as the north Atlantic are strongly influenced by warming due to multi-decadal variability (Edwards et al., 2013 <sup>[[#fn:r431|431]]</sup> ; Harris et al., 2014 <sup>[[#fn:r432|432]]</sup> ), suggesting that there is a longer time-of-emergence of range shifts from natural variability and a need for longer biological time series for robust attribution. The rate of shifts in biogeography of organism is influenced by multiple climatic and non-climatic factors ( ''high confidence'' ) that can result in non-synchronous shifts in community composition ( ''high confidence'' ). There is general under-representation of biogeographical records in low latitudes (Dornelas et al., 2018 <sup>[[#fn:r433|433]]</sup> ), rendering detection and attribution of shifts in biogeography in these regions having ''medium confidence'' . The variation in responses of marine biota to range shifts can cause spatial restructuring of the pelagic ecosystem with consequences for organisms at higher trophic levels (Chivers et al., 2017 <sup>[[#fn:r434|434]]</sup> ; Pecl et al., 2017 <sup>[[#fn:r435|435]]</sup> ) ( ''high confidence'' ). Marine ectotherms have demonstrated some capacity for physiological adjustment and evolutionary adaptation that lowers their sensitivity to warming and decrease in oxygen (Pörtner et al., 2014 <sup>[[#fn:r436|436]]</sup> ; Cavallo et al., 2015 <sup>[[#fn:r437|437]]</sup> ) ( ''low confidence'' ). However, historical responses in abundance and ranges of marine species to ocean warming suggest that adaptation not always suffices to mitigate projected impacts (WGII AR5 Chapter 6) ( ''high confidence'' ).

Marine reptiles, seabirds and mammals breathe air, instead of obtaining oxygen from water, and many of them spend some of their life cycle on land, being their abundance and distribution still affected by temperature (Pörtner et al., 2014 <sup>[[#fn:r438|438]]</sup> ). Long term population changes and shifts in distribution associated with climate change have been observed for temperate species of seabirds and marine mammals (Henderson et al., 2014 <sup>[[#fn:r439|439]]</sup> ; Hiscock and Chilvers, 2014 <sup>[[#fn:r440|440]]</sup> ; Ramp et al., 2015 <sup>[[#fn:r441|441]]</sup> ) ( ''high confidence'' ). For example, Laysan, ''Phoebastria immutabilis,'' and Wandering, ''Diomedea exulans'' , albatross have responded positively to climate change as they have been able to take advantage of the increased intensity of winds. This has allowed them to forage farther and faster, making their foraging trips shorter, increasing their foraging efficiency and breeding success (Descamps et al., 2015 <sup>[[#fn:r442|442]]</sup> ; Thorne et al., 2016 <sup>[[#fn:r443|443]]</sup> ). For reptiles, like sea turtles and snakes, temperature directly affects important life history traits including hatchling size, sex, viability and performance ''(high confidence)'' (Hays et al., 2003 <sup>[[#fn:r444|444]]</sup> ; Pike, 2014 <sup>[[#fn:r445|445]]</sup> ; Dudley et al., 2016 <sup>[[#fn:r446|446]]</sup> ; Santos et al., 2017 <sup>[[#fn:r447|447]]</sup> ). This is particularly important for marine turtles as changing temperatures will affect the hatchling sex ratio because sex is determined by nest site temperature ''(high confidence'' ) (Hatfield et al., 2012 <sup>[[#fn:r448|448]]</sup> ; Santidrián Tomillo et al., 2014 <sup>[[#fn:r449|449]]</sup> ; Patricio et al., 2017 <sup>[[#fn:r450|450]]</sup> ). Loss of breeding substrate, including mostly coastal habitats such as sandy beaches (Section 5.3.3), can reduce the available nesting or pupping habitat for land breeding marine turtles, lizards, seabirds and pinnipeds (Fish et al., 2005 <sup>[[#fn:r451|451]]</sup> ; Fuentes et al., 2010 <sup>[[#fn:r452|452]]</sup> ; Funayama et al., 2013 <sup>[[#fn:r453|453]]</sup> ; Reece et al., 2013 <sup>[[#fn:r454|454]]</sup> ; Katselidis et al., 2014 <sup>[[#fn:r455|455]]</sup> ; Patino-Martinez et al., 2014 <sup>[[#fn:r456|456]]</sup> ; Pike et al., 2015 <sup>[[#fn:r|]]</sup> ; Reynolds et al., 2015; Marshall et al., 2017) ( ''high confidence'' ). Climatic hazards such as SLR contributes to the loss of these coastal habitats (see Section 5.3 and Chapter 3). Changes in ocean temperature will also indirectly impact marine mammals, seabirds and reptiles by changing the abundance and distribution of their prey (Polovina, 2005 <sup>[[#fn:r479|479]]</sup> ; Polovina et al., 2011 <sup>[[#fn:r480|480]]</sup> ; Doney et al., 2012 <sup>[[#fn:r481|481]]</sup> ; Sydeman et al., 2015 <sup>[[#fn:r482|482]]</sup> ; Briscoe et al., 2017 <sup>[[#fn:r483|483]]</sup> ; Woodworth-Jefcoats et al., 2017 <sup>[[#fn:r484|484]]</sup> ) ( ''high confidence'' ). The distributions of some of these large animals is determined by the occurrence and persistence of oceanic bridges and barriers that are related to climate driven processes (Ascani et al., 2016 <sup>[[#fn:r485|485]]</sup> ; McKeon et al., 2016 <sup>[[#fn:r486|486]]</sup> ). For example, the decline of Arctic sea ice is affecting the range and migration patterns of some species and is allowing the exchange of species previously restricted to either the Pacific or Atlantic oceans (Alter et al., 2015 <sup>[[#fn:r487|487]]</sup> ; George et al., 2015 <sup>[[#fn:r488|488]]</sup> ; Laidre et al., 2015 <sup>[[#fn:r489|489]]</sup> ; MacIntyre et al., 2015 <sup>[[#fn:r490|490]]</sup> ; McKeon et al., 2016 <sup>[[#fn:r491|491]]</sup> ; Breed et al., 2017 <sup>[[#fn:r492|492]]</sup> ; Hauser et al., 2017 <sup>[[#fn:r493|493]]</sup> ) (Chapter 3). Also, the range expansion of some of these predatory megafauna can affect species endemic to the habitat; for example, while the decrease in summer sea ice in the Arctic may favour the expansion of killer whales ( ''Orcinus orca'' ), their occurrence can result in narwhale ( ''Monodon monoceros'' ) to avoid the use of key habitats to reduce the risk of killer whales’ predation (Bost et al., 2009 <sup>[[#fn:r459|459]]</sup> ; Sydeman et al., 2015 <sup>[[#fn:r460|460]]</sup> ; Breed et al., 2017 <sup>[[#fn:r461|461]]</sup> ) (see Chapter 3; section 3.2.1.4). In addition, marine mammals, seabirds and sea turtles present habitat requirements associated with bathymetric and mesoscale features that facilitate the aggregation of their prey (Bost et al., 2015 <sup>[[#fn:r462|462]]</sup> ; Kavanaugh et al., 2015 <sup>[[#fn:r463|463]]</sup> ; Hindell et al., 2016 <sup>[[#fn:r464|464]]</sup> ; Hunt et al., 2016 <sup>[[#fn:r465|465]]</sup> ; Santora et al., 2017 <sup>[[#fn:r466|466]]</sup> ). The persistence and location of these features are linked to variations in climate (Crocker et al., 2006 <sup>[[#fn:r467|467]]</sup> ; Baez et al., 2011 <sup>[[#fn:r468|468]]</sup> ; Dugger et al., 2014 <sup>[[#fn:r469|469]]</sup> ; Abrahms et al., 2017 <sup>[[#fn:r470|470]]</sup> ; Youngflesh et al., 2017 <sup>[[#fn:r471|471]]</sup> ) and to foraging success, juvenile recruitment, breeding phenology, growth rates and population stability (Costa et al., 2010 <sup>[[#fn:r472|472]]</sup> ; Ancona and Drummond, 2013 <sup>[[#fn:r473|473]]</sup> ; Ducklow et al., 2013 <sup>[[#fn:r474|474]]</sup> ; Chambers et al., 2014 <sup>[[#fn:r475|475]]</sup> ; Descamps et al., 2015 <sup>[[#fn:r476|476]]</sup> ; Abadi et al., 2017 <sup>[[#fn:r477|477]]</sup> ; Bjorndal et al., 2017 <sup>[[#fn:r478|478]]</sup> ; Fluhr et al., 2017; Youngflesh et al., 2017) ( ''high confidence'' ). Overall, recent evidence further support that impacts of climate change on some marine reptiles, mammals and birds have been observed in recent decades ( ''high confidence'' ) and that the direction of impacts vary between species, population and geographic locations (Trivelpiece et al., 2011; Hazen et al., 2013; Clucas et al., 2014; Constable et al., 2014; George et al., 2015) ( ''high confidence'' ).

Warming has contributed also to observed changes in phenology (timing of repeated seasonal activities) of marine organisms (Gittings et al., 2018 <sup>[[#fn:r505|505]]</sup> ), although observations are biased towards the northeast Atlantic (Poloczanska et al., 2016 <sup>[[#fn:r506|506]]</sup> ; Thackeray et al., 2016). Shifts in the timing of interacting species have occurred in the last decades, eventually leading to uncoupling between prey and predators, with cascading community and ecosystem consequences (Kharouba et al., 2018; Neuheimer et al., 2018 <sup>[[#fn:r507|507]]</sup> ). Timing of spring phenology of marine organisms is shifting to earlier in the year under warming, at an average rate of 4.4 ± 1.1 days per decade (Poloczanska et al., 2013 <sup>[[#fn:r508|508]]</sup> ), although it is variable among taxonomic groups and among ocean regions (Lindley and Kirby, 2010 <sup>[[#fn:r509|509]]</sup> ). This is consistent with the expectations based on the close relationship between temperature and these biological events, supporting evidence from AR5 (Bruge et al., 2016 <sup>[[#fn:r510|510]]</sup> ; Poloczanska et al., 2016 <sup>[[#fn:r511|511]]</sup> ). Thus, the growing amount of literature and new studies since AR5 WGII and SR15 further support   that phenology of marine ectotherms in the epipelagic systems are related to ocean warming ( ''high confidence'' ) and that the timing of biological events has shifted earlier ( ''high confidence'' ).

''Observed impacts of multiple climatic hazards''

WGII AR5 concludes that multiple climatic hazards from ocean acidification, hypoxia and decrease in nutrient and food supplies pose risks to marine ecosystems, and the risk can be elevated when combined with warming (Riebesell and Gattuso, 2014 <sup>[[#fn:r512|512]]</sup> ; Gattuso et al., 2015 <sup>[[#fn:r513|513]]</sup> ). In a recent meta-analysis of 632 published experiments, primary production by temperate non-calcifying plankton increases with elevated temperature and CO 2 , whereas tropical plankton decreases productivity because of acidification (Nagelkerken and Connell, 2015 <sup>[[#fn:r514|514]]</sup> ). Also, temperature increases consumption and metabolic rates of herbivores but not secondary production; the latter decreases with acidification in calcifying and non-calcifying species. These effects together create a mismatch with carnivores whose metabolic and foraging costs increase with temperature (Nagelkerken and Connell, 2015 <sup>[[#fn:r515|515]]</sup> ). Warming may also exacerbate the effects of ocean acidification on the rate of photosynthesis in phytoplankton (Lefevre, 2016 <sup>[[#fn:r516|516]]</sup> ). There is some, but limited, reports of observed impacts on calcified pelagic organisms that are attributed to secular trend in ocean acidification and warming (Harvey et al., 2013 <sup>[[#fn:r517|517]]</sup> ; Kroeker et al., 2013 <sup>[[#fn:r518|518]]</sup> ; Nagelkerken et al., 2015 <sup>[[#fn:r519|519]]</sup> ; Boyd et al., 2016 <sup>[[#fn:r520|520]]</sup> ). For example , Rivero-Calle et al. (2015) reported, using CPR archives, that stocks of coccolithophores (a group of phytoplankton that forms calcium carbonate plateles) have increased by 2% to over 20% in the north Atlantic over the last five decades, and that this increase is linked to synergistic effects of increasing anthropogenic CO 2 and rising temperatures, as supported by their statistical analysis and a number of experimental studies. Most of the available evidence supports that ocean acidification and hypoxia can act additively or synergistically between each other and with temperature across different groups of biota (Figure 5.13). Limitation of nutrient and food availability and predation pressures can further increase the sensitivity of organismal groups to climate change in specific ecosystems (Riebesell et al., 2017 <sup>[[#fn:r494|494]]</sup> ). Climate change also affects organisms indirectly through the impacts on competitiveness between organisms that favour those that are more adaptive to the changing environmental conditions (Alguero-Muniz et al., 2017 <sup>[[#fn:r495|495]]</sup> ) and changes in trophic interactions (Seebacher et al., 2014 <sup>[[#fn:r496|496]]</sup> ). Overall, direct ''in situ'' observations and laboratory experiments show that there are significant responses to the multiple stressors of warming, ocean acidification and low oxygen on phytoplankton, zooplankton and fishes and that these responses can be additive or synergistic ( ''high confidence,'' Figure 5.13).

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===== 5.2.3.1.2 Future changes in the epipelagic ocean =====

WGII AR5 and SR15 conclude that projected ocean warming will continue to cause poleward shifts in the distribution and biomass of pelagic species, paralleled by altered seasonal timing of their activities, species abundance, migration pattern and reduction in body size in the 21st century under scenarios of increasing greenhouse gas emission (Pörtner et al., 2014 <sup>[[#fn:r497|497]]</sup> ; Hoegh-Guldberg et al., 2018 <sup>[[#fn:r498|498]]</sup> ). Simultaneously, projected expansion of OMZ and ocean acidification could lead to shifts in community composition toward hypoxia-tolerant and non-calcified organisms, respectively. However, these projected biological changes in the ocean raise questions about how individuals, communities and food webs will respond to the multiple impacts from climatic and non-climatic stressors in the future, and the feedbacks of the effects of their ecological impacts on modifying the physical and biogeochemical conditions of the ocean (Schaum et al., 2013 <sup>[[#fn:r499|499]]</sup> ; Boyd et al., 2016 <sup>[[#fn:r500|500]]</sup> ; O’Brien et al., 2016 <sup>[[#fn:r501|501]]</sup> ; Moore, 2018 <sup>[[#fn:r502|502]]</sup> ). This section focuses on addressing these questions in order to assess the future risk of impacts of climate change on the epipelagic ecosystem.

''Future projections on phytoplankton distribution, community structure and biomass''

While analysis of outputs from CMIP5 ESMs project that global average NPP and biomass of phytoplankton community will decrease in the 21st century under RCP2.6 and RCP8.5 (see Section 5.2.2.6). However, the future risk of impacts of epipelagic ecosystem can also depend on changes in community structure of phytoplankton species. Barton et al. (2016) projected the biogeography of 87 taxa of phytoplankton (diatoms and dinoflagellates) in the north Atlantic to 2051–2100 relative to the past (1951–2000) with scenarios of changes in temperature and other ocean conditions such as salinity, density and nutrients under RCP8.5. The study found that 74% of the studied taxa exhibit a poleward shift at a median rate of 12.9 km per decade, but 90% of the taxa shift eastward at a median rate of 42.7 km per decade. Such changes may affect food webs and biogeochemical cycles, and with consequence to the productivity of living marine resources (Stock et al., 2014 <sup>[[#fn:r503|503]]</sup> ; Barton et al., 2016 <sup>[[#fn:r504|504]]</sup> ).

Outputs from CMIP5 ESMs suggest that projected warming and reduction in nutrient availability in low latitudes, as a result of increasing stratification of the ocean under climate change, will increase the dominance of small-sized phytoplankton, growing more efficiently than larger taxa at low nutrient levels (Dutkiewicz et al., 2013b <sup>[[#fn:r522|522]]</sup> ). Dominant groups in subtropical oceans, like the picoplanktonic cyanobacteria ''Synechococcus'' and ''Prochlorococcus'' , are projected to expand their range of distribution towards higher latitudes and increase their abundances by 14–29%, respectively, under a future warmer ocean (Flombaum et al., 2013 <sup>[[#fn:r523|523]]</sup> ), although synergistic effects of warming and CO 2 on photosynthetic rates could lead to a dominance of ''Synechococcus'' over ''Prochlorococcus'' (Fu et al., 2007 <sup>[[#fn:r524|524]]</sup> ) ( ''low confidence'' ). Similarly, temperature-driven range shifts towards higher latitudes are also likely for tropical diazotrophic (N 2 -fixing) cyanobacteria, although they could disappear from parts of their current tropical ranges where future warming may exceed their maximum thermal tolerance limits (Hutchins and Fu, 2017 <sup>[[#fn:r525|525]]</sup> ) ( ''low confidence'' ). Modelling experiments show that the effects of warming on phytoplankton community will be exacerbated by ocean acidification at levels expected in the 21st century for RCP8.5, leading to increasing growth rate responses of some phytoplankton groups, such as diazotrophs and ''Synechococcus'' , with predicted increases in biomass up to 10% in tropical and subtropical waters (Dutkiewicz et al., 2015 <sup>[[#fn:r526|526]]</sup> ) ( ''low confidence'' ). Furthermore, warming is projected to interact with decreasing oxygen levels and increases in iron in the nutrient-impoverished subtropical waters, favoring the dominance of the diazotrophic colonial cyanobacteria ''Trichodesmium'' (Sohm et al., 2011 <sup>[[#fn:r527|527]]</sup> ; Boyd et al., 2013 <sup>[[#fn:r528|528]]</sup> ; Ward et al., 2013 <sup>[[#fn:r529|529]]</sup> ; Hutchins and Fu, 2017 <sup>[[#fn:r530|530]]</sup> ) ( ''medium confidence'' ).

Regional differences in the changes in phytoplankton community and their impacts on epipelagic ecosystem are however complex and depends on multiple interactions of co-varying climate change stressors at regional level (Boyd and Hutchins, 2012 <sup>[[#fn:r531|531]]</sup> ). Based on global ocean model simulations, Boyd et al. (2015b) show that the interaction between warming, increased CO 2 and a decline in phosphate and silicate would benefit coccolithophores against diatoms in the northern north Atlantic, despite decreasing rates of calcification. Evidence, based on long-term experiments of acclimation or adaptation to increasing temperatures in combination with elevated CO 2 , show that individual growth and carbon fixation rates of coccolithophores at high CO 2 are modulated by temperature, light, nutrients and UV radiation, and could increase calcification while the responses are also species-specific (Lohbeck et al., 2012 <sup>[[#fn:r532|532]]</sup> ; Khanna et al., 2013 <sup>[[#fn:r533|533]]</sup> ). Calcification of planktonic foraminifera will be however negatively affected by acidification (Roy et al., 2015 <sup>[[#fn:r535|535]]</sup> ), and their populations are predicted to experience the greatest decrease in diversity and abundance in sub-polar and tropical areas, under RCP8.5 (Brussaard et al., 2013 <sup>[[#fn:r535|535]]</sup> ), however environmental controls of calcite production by foraminifera are still poorly understood ( ''low confidence'' ). Boyd et al. (2015b) analysis indicate also that diatoms would benefit from the synergistic effects of increased warming and iron supply in the northern Southern Ocean, as supported by laboratory experiments and field studies with polar diatoms (Rose et al., 2009 <sup>[[#fn:r536|536]]</sup> ) ( ''low confidence)'' . At low-latitude provinces, projected concurrent increases of CO 2 and iron, and decreases in both nitrate and phosphate supply, may favour nitrogen fixers, but with ocean regional variability, since iron is thought to limit N 2 fixation in the eastern Pacific and phosphorus in the Atlantic Ocean (Gruber, 2019 <sup>[[#fn:r537|537]]</sup> ; Wang et al., 2019 <sup>[[#fn:r538|538]]</sup> ). However, recent experimental work with the diazotrophic colonial ''Trichodesmium'' and the unicellular ''Crocosphaera'' have shown a broad range of responses from rising CO 2 , with either increases or decreases in N 2 fixation rates, and with mixed evidence on co-limiting processes (Eichner et al., 2014 <sup>[[#fn:r539|539]]</sup> ; Garcia et al., 2014 <sup>[[#fn:r540|540]]</sup> ; Gradoville et al., 2014 <sup>[[#fn:r541|541]]</sup> ; Walworth et al., 2016 <sup>[[#fn:r542|542]]</sup> ; Hong et al., 2017 <sup>[[#fn:r543|543]]</sup> ; Luo et al., 2019 <sup>[[#fn:r5|5]]</sup> 44) ( ''low confidence'' ).

Overall, the response of phytoplankton to the interactive effects of multiple drivers is complex, and presently ESMs do not resolve the full complexity of their physiological responses (Breitberg et al., 2015 <sup>[[#fn:r545|545]]</sup> ; Hutchins and Boyd, 2016 <sup>[[#fn:r546|546]]</sup> ; O’Brien et al., 2016 <sup>[[#fn:r547|547]]</sup> ), precluding a clear assessment of the effects of these regional distinctive multi-stressor patterns ( ''high confidence'' ).

''Future projections on zooplankton distribution and biomass''

An ensemble of 12 CMIP5 ESMs project average declines of 6.4 ± 0.79% (95% confident limits) and 13.6 ± 1.70%) in zooplankton biomass in the 21st century relative to 1990 – 1999 historical values under RCP2.6 and RCP8.5 (Kwiatkowski et al., 2019 <sup>[[#fn:r548|548]]</sup> ). Also, production of mesozooplankton is projected from a single ESM to decrease by 7.9% between 1951 – 2000 and 2051 – 2100 under RCP8.5 (Stock et al., 2014 <sup>[[#fn:r549|549]]</sup> ). Such projected decreases in zooplankton biomass and production are partly contributed by climate-induced reduction in phytoplankton production and trophic transfer efficiency particularly in low-latitude ecosystems (Stock et al., 2014 <sup>[[#fn:r550|550]]</sup> ) (5.2.2.6). The impacts may be larger than these projections if changes in the relative abundance of carbon, nitrogen and phosphorus are considered by the models (Kwiatkowski et al., 2019 <sup>[[#fn:r551|551]]</sup> ). The overall projected decrease in zooplankton biomass is characterised by a strong latitudinal differences, with the largest decrease in tropical regions and increase in the polar regions, particularly the Arctic Ocean (Chust et al., 2014 <sup>[[#fn:r552|552]]</sup> ; Stock et al., 2014 <sup>[[#fn:r553|553]]</sup> ; Kwiatkowski et al., 2019 <sup>[[#fn:r554|554]]</sup> ) (Chapter 3) ( ''high agreement'' ). However, the projected increase in zooplankton biomass in the polar region may be affected by the seasonality of light cycle at high latitudes that may limit the bloom season at high latitude (Sundby et al., 2016 <sup>[[#fn:r555|555]]</sup> ). The projected decrease in zooplankton abundance, particularly in tropical regions, can impact marine organisms higher in the foodweb, including fish populations that are important to fisheries (Woodworth-Jefcoats et al., 2017 <sup>[[#fn:r556|556]]</sup> ). Therefore, there is ''high agreement'' in model projections that global zooplankton biomass will ''very likely'' reduce in the 21st century, with projected decline under RCP8.5 almost doubled that of RCP2.6 ( ''very likely'' ). However, the strong dependence of the projected declines on phytoplankton production ( ''low confidence'' , 5.2.2.6) and simplification in representation of the zooplankton communities and foodweb render their projections having ''low confidence'' .

Future responses of zooplankton species and communities to climate change are however affected by interactions between multiple climatic drivers. Experiments in laboratory show that acidification could partly counteract some observed effects of increased temperature on zooplankton, although the level and direction of the biological responses vary largely between species (Mayor et al., 2015 <sup>[[#fn:r557|557]]</sup> ; Garzke et al., 2016 <sup>[[#fn:r558|558]]</sup> ), with results ranging from no effects (Weydmann et al., 2012 <sup>[[#fn:r559|559]]</sup> ; McConville et al., 2013 <sup>[[#fn:r560|560]]</sup> ; Cripps et al., 2014 <sup>[[#fn:r561|561]]</sup> ; Alguero-Muniz et al., 2016 <sup>[[#fn:r562|562]]</sup> ; Bailey et al., 2016 <sup>[[#fn:r563|563]]</sup> ), to negative effects (Lischka et al., 2011 <sup>[[#fn:r564|564]]</sup> ; Cripps et al., 2014 <sup>[[#fn:r565|565]]</sup> ; Alguero-Muniz et al., 2017 <sup>[[#fn:r566|566]]</sup> ) or positive effects (Alguero-Muniz et al., 2017 <sup>[[#fn:r567|567]]</sup> ; Taucher et al., 2017 <sup>[[#fn:r568|568]]</sup> ). These differences in response can affect trophic interactions between zooplankton species ; for example, some predatory non-calcifying zooplankton may perform better under warmer and lower pH conditions, leading to increased predation on other zooplankton species (Caron and Hutchins, 2012 <sup>[[#fn:r569|569]]</sup> ; Winder et al., 2017 <sup>[[#fn:r570|570]]</sup> ). Therefore, the large variation in sensitivity between zooplankton to future conditions of warming and ocean acidification suggests elevated risk on community structure and inter-specific interactions of zooplankton in the 21st century ( ''medium confidence'' ). Consideration of these species-specific responses may further modify the projected changes in zooplankton biomass by ESMs (Boyd et al., 2015a <sup>[[#fn:r571|571]]</sup> ).

'' Future projections on fish distribution, size and biomass''

Recent model projections since AR5 and SR15 continue to support global-scale range shifts of marine fishes at rates of tens to hundreds of km per decade in the 21st century, with rate of shifts being substantially higher under RCP8.5 than RCP2.6 (Jones and Cheung, 2015 <sup>[[#fn:r572|572]]</sup> ; Robinson et al., 2015 <sup>[[#fn:r573|573]]</sup> ; Morley et al., 2018 <sup>[[#fn:r574|574]]</sup> ). Globally, the general direction of range shifts of epipelagic fishes is poleward (Jones and Cheung, 2015 <sup>[[#fn:r575|575]]</sup> ; Robinson et al., 2015 <sup>[[#fn:r576|576]]</sup> ), while the projected directions of regional and local range shifts generally follow temperature gradients (Morley et al., 2018 <sup>[[#fn:r577|577]]</sup> ). Polewards range shifts are projected to result in decreases in species richness in tropical oceans, and increases in mid to high-latitude regions leading to global-scale species turnover (sum of species local extinction and expansion) (Ben Rais Lasram et al., 2010; Jones and Cheung, 2015 <sup>[[#fn:r578|578]]</sup> ; Cheung and Pauly, 2016 <sup>[[#fn:r579|579]]</sup> ; Molinos et al., 2016 <sup>[[#fn:r580|580]]</sup> ) ( ''medium confidence'' on trends, ''low confidence'' on magnitude because of model uncertainties and limited number of published model simulations). For example, species turnover relative to their present day richness in the tropical oceans (30 o N–30 o S) is projected to be 14–21% and 37–39% by 2031–2050 and 2081–2100 under RCP8.5 (ranges of mean projections from two sets of simulation for marine fish distributions) (Jones and Cheung, 2015 <sup>[[#fn:r581|581]]</sup> ; Molinos et al., 2016 <sup>[[#fn:r582|582]]</sup> ). In contrast, high-latitude regions (&gt;60 o N–60 o S) is projected to have higher rate of species turnover than the tropics (an average of 48% between the two data sets for region &gt;60 o N). The high species turnover in the Arctic is explained by species’ range expansion from lower-latitude and the relatively lower present day fish species richness in the Arctic. The projected intensity of species turnover is lower under lower emission scenarios (Jones and Cheung, 2015 <sup>[[#fn:r583|583]]</sup> ; Molinos et al., 2016 <sup>[[#fn:r584|584]]</sup> ) (see also Section 5.4.1) ( ''high confidence'' ). Projections from multiple fish species distribution models show hotspots of decrease in species richness in the Indo-Pacific region, and semi-enclosed seas such as the Red Sea and Persian Gulf (Cheung et al., 2013 <sup>[[#fn:r585|585]]</sup> ; Burrows et al., 2014 <sup>[[#fn:r586|586]]</sup> ; García Molinos et al., 2015 <sup>[[#fn:r587|587]]</sup> ; Jones and Cheung, 2015 <sup>[[#fn:r588|588]]</sup> ; Wabnitz et al., 2018 <sup>[[#fn:r589|589]]</sup> ) ( ''medium evidence'' , ''high agreement'' ). In addition, geographic barriers such as land boundaries in the poleward species range edge in semi-enclosed seas or lower oxygen water in deeper waters are projected to limit range shifts, resulting in larger relative decrease in species richness ( ''medium confidence'' ) (Cheung et al., 2013 <sup>[[#fn:r590|590]]</sup> ; Burrows et al., 2014 <sup>[[#fn:r591|591]]</sup> ; García Molinos et al., 2015 <sup>[[#fn:r592|592]]</sup> ; Jones and Cheung, 2015 <sup>[[#fn:r593|593]]</sup> ; Rutterford et al., 2015 <sup>[[#fn:r594|594]]</sup> ).

Warming and decrease in oxygen content is projected to impact growth of fishes, leading to reduction in body size and contraction of suitable environmental conditions (Deutsch et al., 2015 <sup>[[#fn:r595|595]]</sup> ; Pauly and Cheung, 2017 <sup>[[#fn:r596|596]]</sup> ), with the intensity of impacts being directly related to the level of climate change. The projected reduction in abundance of larger-bodied fishes could reduce predation and exacerbate the increase in dominance of smaller-bodied fishes in the epipelagic ecosystem (Lefort et al., 2015 <sup>[[#fn:r597|597]]</sup> ). Fishes exposed to ocean acidification level expected under RCP8.5 showed impairments of sensory ability and alteration of behaviour including olfaction, hearing, vision, homing and predator avoidance (Kroeker et al., 2013 <sup>[[#fn:r598|598]]</sup> ; Heuer and Grosell, 2014 <sup>[[#fn:r599|599]]</sup> ; Nagelkerken et al., 2015 <sup>[[#fn:r600|600]]</sup> ). The combined effects of warming, ocean deoxygenation and acidification in the 21st century are projected to exacerbate the impacts on the body size, growth, reproduction and mortality of fishes, and consequently increases their risk of population decline ( ''medium evidence, high agreement, high confidence'' ).

<span id="table-5.3"></span>
<!-- START TABLE -->
'''Table 5.3'''

Projected changes in total animal biomass by the mid- and end- of the 21st century under Representative Concentration Pathway (RCP)2.6 and RCP8.5. Total animal biomass is based on 10 sets of projections for each RCP under the Fisheries and Marine Ecosystems Impact Model Intercomparison Project (FISMIP) (Lotze et al. 2018 <sup>[[#fn:r601|601]]</sup> ). The very likely ranges of the projections (95% confidence intervals) are provided. Reference period is 1986–2005.

<!-- TABLE -->
{| class="wikitable"
|-
|
| colspan="4"| '''Total animal biomass (%)'''
|-
|
| colspan="2"| '''RCP2.6'''
| colspan="2"| '''RCP8.5'''
|-
| '''Region'''
| '''2031''' – '''2050'''
| '''2081''' – '''2100'''
| '''2031''' – '''2050'''
| '''2081''' – '''2100'''
|-
| '''&gt;60''' '''o''' '''N'''
| 8.4 ± 9.3
| 8.5 ± 13.7
| 7 ± 9.2
| –1.1 ± 20.2
|-
| '''30''' '''o''' '''N''' – '''50''' '''o''' '''N'''
| –8.1 ± 4
| –4.5 ± 3.6
| –10.1 ± 4.7
| –21.3 ± 9.4
|-
| '''30''' '''o''' '''N''' – '''30''' '''o''' '''S'''
| –7.2 ± 2.7
| –7.3 ± 3.1
| –9 ± 3.6
| –23.2 ± 9.5
|-
| '''30''' '''o''' '''S''' – '''50''' '''o''' '''S'''
| –3.3 ± 2.1
| –3.5 ± 2.5
| –4.2 ± 2.9
| –9 ± 9.8
|-
| '''&lt;60''' '''o''' '''S'''
| 1.7 ± 4.5
| –0.9 ± 2.9
| 0.7 ± 3.9
| 12.4 ±11.9
|}
<!-- END TABLE -->

An ensemble of global-scale marine ecosystem and fisheries models that are part of the Fisheries and Marine Ecosystems Impact Models Intercomparison Project (FISHMIP) undertook coordinated simulation experiments and projected future changes in marine animals (mainly invertebrate and fish) globally under climate change (Lotze et al., 2018 <sup>[[#fn:r602|602]]</sup> ). These models represent marine biota and ecosystems differently, ranging from population-based to functional traits- and size-based structure and their responses are driven primarily by temperature and NPP, although oxygen, salinity and ocean advection are considered in a subset of models and play a secondary role in affecting the projected changes in biomass (Blanchard et al., 2012 <sup>[[#fn:r603|603]]</sup> ; Fernandes et al., 2013 <sup>[[#fn:r604|604]]</sup> ; Carozza et al., 2016 <sup>[[#fn:r605|605]]</sup> ; Cheung et al., 2016a <sup>[[#fn:r606|606]]</sup> ). Overall, potential total marine animal biomass is projected to decrease by 4.3 ± 2.0% (95% confident intervals) and 15.0 ± 5.9% under RCP2.6 and RCP8.5, respectively, by 2080–2099 relative to 1986–2005, while the decrease is around 4.9% by 2031-2050 across all RCP2.6 and RCP8.5 ( ''very'' ''likely'' ) (Figure 5.14). Accounting for the removal of biomass by fishing exacerbates the decrease in biomass for large-bodied animals which are particularly sensitive to fishing ( ''likely'' for the direction of changes). Regionally, total animal biomass decreases largely in tropical and mid-latitude oceans ( ''very'' ''likely'' ) (Table 5.3, Figure 5.14) (Bryndum-Buchholz et al., 2019 <sup>[[#fn:r607|607]]</sup> ). The high uncertainty and the ''low confidence'' in the projection in the Arctic Ocean (Chapter 3) is because of the large variations in simulation results for this region between the ESMs and between the FISHMIP models, as well as the insufficient understanding of the oceanographic changes and their biological implications in the Arctic Ocean. In the Southern Ocean, the decrease in consumer biomass is mainly in the southern Indian Ocean while other parts of the Southern Ocean are projected to have an increase in animal biomass by 2100 under RCP8.5, reflecting mainly the projected pattern of changes in NPP from the ESMs (see Section 5.2.2.6).

<span id="figure-5.14"></span>
<!-- START IMG -->
<!-- IMG TITLE -->
'''Figure 5.14'''

<span id="figure-5.14-projected-changes-in-total-animal-biomass-including-fishes-and-invertebrates-based-on-outputs-from-10-sets-of-projections-for-each-representative-concentration-pathway-rcp-from-the-fisheries-and-marine-ecosystems-impact-model-intercomparison-project-fismip-www.isimip.orggettingstartedmarine--ecosystems-fisheries-lotze-et-al.-2018-a-b-multi-model-mean-change-in-un-fished-total-marine-animal"></span>
<!-- IMG CAPTION -->
'''Figure 5.14 | Projected changes in total animal biomass (including fishes and invertebrates) based on outputs from 10 sets of projections for each Representative Concentration Pathway (RCP) from the Fisheries and Marine Ecosystems Impact Model Intercomparison Project (FISMIP, www.isimip.org/gettingstarted/marine- ecosystems-fisheries) (Lotze et al. 2018); (a, b) multi-model mean change (%) in un-fished total marine animal […]'''
<!-- IMG FILE -->
[[File:6b80fa762b7c8eed204f59ee42320efe IPCC-SROCC-CH_5_14-1.jpg]]

Figure 5.14 | Projected changes in total animal biomass (including fishes and invertebrates) based on outputs from 10 sets of projections for each Representative Concentration Pathway (RCP) from the Fisheries and Marine Ecosystems Impact Model Intercomparison Project (FISMIP, www.isimip.org/gettingstarted/marine- ecosystems-fisheries) (Lotze et al. 2018); (a, b) multi-model mean change (%) in un-fished total marine animal biomass in 2085–2099 relative to 1986–2005 under RCP2.6 and RCP8.5, respectively. Dotted area represents 8 out of 10 sets of model projections agree in the direction of change (c) projected change in global total animal biomass from 1970 to 2099 under RCP2.6 (red) and RCP8.5 (blue). Variability among different ecosystem and Earth-system model combinations (n=10) expressed as the very likely range (95% confidence interval).

''Future projections on epipelagic components of the biological pump''

A wide range of studies, from laboratory experiments, mesocosm enclosures, synthesis of observations to modeling experiments, provide insights into how the multi-faceted components of the ‘biological pump’ (the physical and biologically mediated processes responsible for transporting organic carbon from the upper ocean to depth) are projected to be altered in the coming decades. A synthesis of the individual components reported to both influence the performance of the biological pump, and which are sensitive to changing ocean conditions, is presented in Table 5.4. The table lists the putative controlling of each environmental factor, such as warming, that influences the biological pump, and the reported modification (where available) of each individual factor by changing ocean conditions for both the epipelagic ocean and the deep ocean. Analyses of long-term trends in primary production and particle export production, as well as model simulations, reveal that increasing temperatures, leading to enhanced stratification and nutrient limitation, will have the greatest influence on decreasing the flux of particulate organic carbon (POC) to the deep ocean (Bopp et al., 2013 <sup>[[#fn:r608|608]]</sup> ; Boyd et al., 2015a <sup>[[#fn:r609|609]]</sup> ; Fu et al., 2016 <sup>[[#fn:r610|610]]</sup> ; Laufkötter et al., 2016 <sup>[[#fn:r611|611]]</sup> ). However, different lines of evidence (including observation, modeling and experimental studies) provide ''low confidence'' on the mechanistic understanding of how climatic drivers affect different components of the biological pump in the epipelagic ocean, as well as changes in the efficiency and magnitude of carbon export in the deep ocean (see section below and Table 5.4); this renders the projection of future contribution of the biological carbon pump to the export of POC to the deep ocean having ''low confidence'' .

<!-- END IMG -->
<span id="table-5.4"></span>
<!-- START TABLE -->
'''Table 5.4'''

Projected future changes to the ocean biological pump (adapted from Boyd et al. (2015a)). Environmental controls on individual factors that influence downward POC flux are based on published reports from experiments (denoted by '''E''' ), modelling simulations ( '''M''' ) and observations ( '''O''' ). In some cases, due to the paucity, and regional specificity, of published reports it has been indicated the sign of the projected change on export (in italics), as opposed to the magnitude. NPP: Net Primary Production; POC: Particulate Organic Carbon; DOC: Dissolved Organic Carbon; TEP: Transparent Exopolymer Particles; OA: Ocean Acidification. Climate change denotes multiple controls such as nutrients, temperature and irradiance, as parameterised in coupled ocean atmosphere models. *denotes observation for low latitudes only. '''**''' represents major uncertainty over environmental modulation of this component of the biological pump. ***denotes joint influence of temperature and acidification.

<!-- TABLE -->
{| class="wikitable"
|-
| '''Pump component'''
| '''Oceanic driver'''
| '''Projected change (by year 2100)'''
| '''Confidence'''
| '''References &amp; Lines of evidence'''
|-
| '''Epipelagic Ocean'''
|
|-
| Phytoplankton growth
| Temperature (warming)
| ~10% Faster (nutrient-replete) no change (nutrient-deplete)
| High
| (Boyd et al., 2013 <sup>[[#fn:r613|613]]</sup> ) '''E''' ; (Maranon et al., 2014 <sup>[[#fn:r614|614]]</sup> ) '''O*'''
|-
| NPP
| Climate change (temperature, nutrients, CO 2 )
| 10 – 20% decrease (low latitudes);
10 – 20% increase (high latitudes)

| Medium
| (Bopp et al., 2013) '''M'''
|-
| Partitioning of NPP (POC, TEP, DOC)
| OA
| ~20% increase in TEP production
| Medium
| (Engel et al., 2014 <sup>[[#fn:r615|615]]</sup> ) '''E''' ; (Riebesell et al., 2007 <sup>[[#fn:r616|616]]</sup> ) '''E''' ; (Seebah et al., 2014 <sup>[[#fn:r617|617]]</sup> ) '''E'''
|-
| Food web retention of NPP
| OA
| Enhanced transfer of organic matter to higher trophic levels, reduced N and P sedimentation by 10%
| Low
| (Boxhammer et al., 2018) '''E'''
|-
| Floristic shifts
| Climate change (warming, salinity, OA, iron)
| Shift to smaller or larger cells
( ''less export vs more export; inconclusive'' )

| Low
| (Moràn et al., 2010 <sup>[[#fn:r618|618]]</sup> ) '''O''' ; (Li et al., 2009 <sup>[[#fn:r619|619]]</sup> ) '''O;''' (Dutkiewicz et al., 2013a <sup>[[#fn:r620|620]]</sup> ) '''M;''' (Tréguer et al., 2018 <sup>[[#fn:r621|621]]</sup> ) '''O;''' (Sett et al., 2014 <sup>[[#fn:r622|622]]</sup> ) '''E'''
|-
| Differential susceptibility
| Temperature (warming)
| Growth-rate of grazers more temperature dependent than prey
( ''less export'' )

| Low
| (Rose and Caron, 2007 <sup>[[#fn:r626|626]]</sup> ) '''O'''
|-
| Bacterial hydrolytic effects
| Warming, OA
| Increase under warming and low pH (variable response in different plankton communities)
| Low
| (Burrell et al., 2017 <sup>[[#fn:r623|623]]</sup> ) '''E'''
|-
| Grazer physiological responses
| Warming
| Copepods had faster respiration and ingestion rates, but higher mortality
( ''inconclusive'' )

| Low
| (Isla et al., 2008 <sup>[[#fn:r627|627]]</sup> ) '''E'''
|-
| Faunistic shifts
| Temperate and subpolar zooplankton species shifts
| Temperature
( ''inconclusive'' )

| Low
| (Edwards et al., 2013 <sup>[[#fn:r628|628]]</sup> ) '''O'''
|-
| Food web amplification
| Warming
| Zooplankton negatively amplify the climate change signal that propagates up from phytoplankton in tropical regions, and positively amplify in polar regions
| Low
| (Chust et al., 2014) '''M''' ; (Stock et al., 2014) '''M'''
|-
| '''Deep Ocean'''
|
|-
| Bacterial hydrolytic enzyme activity
| Temperature
| 20% increase (resource-replete) to no change (resource-deplete)
| Low
| (Wohlers-Zöllner et al., 2011 <sup>[[#fn:r642|642]]</sup> ) '''E''' ; (Endres et al., 2014 <sup>[[#fn:r643|643]]</sup> ) '''E''' ; (Bendtsen et al., 2015 <sup>[[#fn:r644|644]]</sup> ) '''E''' ; (Piontek et al., 2015) '''E***'''
|-
| Particle sinking rates (viscosity)
| Warming
| 5% faster sinking/°C warming
| Low
| (Taucher et al., 2014) '''M'''
|-
| Mesozooplankton community composition
| Temperature '''**'''
| Shifts which increase/decrease
particle transformations

( ''less/more export, respectively'' )

| Low
| (Burd and Jackson, 2002 <sup>[[#fn:r646|646]]</sup> ) M ; (Ikeda et al., 2001 <sup>[[#fn:r647|647]]</sup> ) '''O'''
|-
| Vertical migrators
| Climate change (irradiance, temperature)
| ( ''more export'' )
| Low
| (Almén et al., 2014) '''O''' ; (Berge et al., 2014) '''O'''
|-
| Deoxygenation
| Climate change
| ( ''more export'' )
| Low
| (Rykaczewski and Dunne, 2010 <sup>[[#fn:r648|648]]</sup> ) '''M''' ; (Cocco et al., 2013 <sup>[[#fn:r649|649]]</sup> ) '''O;''' (Hofmann and Schellnhuber, 2009 <sup>[[#fn:r650|650]]</sup> ) '''M'''
|}
<!-- END TABLE -->

<div id="section-5-2-3-2the-deep-pelagic-ocean"></div>

<span id="the-deep-pelagic-ocean"></span>