Editing IPCC:AR6/WGI/Chapter-1 (section)

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Observations of the ocean have expanded significantly since AR5, with expanded global coverage of in situ ocean temperature and salinity observations, in situ ocean biogeochemistry observations, and satellite retrievals of a variety of EOVs. Many recent advances are extensively documented in a compilation by [[#Lee--2019|Lee et al. (2019)]] . Below we discuss those most relevant for the current assessment.

Argo is a global network of nearly 4000 autonomous profiling floats ( [[#Roemmich--2019|Roemmich et al., 2019]] ), delivering detailed constraints on the horizontal and vertical structure of temperature and salinity across the global ocean. Argo has greatly expanded since AR5, including biogeochemistry and measurements deeper than 2000 m ( [[#Jayne--2017|Jayne et al., 2017]] ), and the longer time series enable more rigorous climate assessments of direct relevance to estimates of ocean heat content (Sections 2.3.3.1 and 7.2.2.2). Argo profiles are complemented by animal-borne sensors in several key areas, such as the seasonally ice-covered sectors of the Southern Ocean ( [[#Harcourt--2019|Harcourt et al., 2019]] ).

Most basin-scale arrays of moored ocean instruments have expanded since AR5, providing decades-long records of the ocean and atmosphere properties relevant for climate, such as the El Niño–Southern Oscillation ( [[#Chen--2018|Chen et al., 2018]] ), deep convection ( [[#de%20Jong--2018|de Jong et al., 2018]] ) or transports through straits ( [[#Woodgate--2018|Woodgate, 2018]] ). Key basin-scale arrays include transport-measuring arrays in the Atlantic Ocean, continuing ( [[#McCarthy--2020|McCarthy et al., 2020]] ) or newly added since AR5 ( [[#Lozier--2019|Lozier et al., 2019]] ), supporting the assessment of regional ocean circulation (Section 9.2.3). Tropical ocean moorings in the Pacific, Indian and Atlantic oceans include new sites, improved capability for real-time transmission, and new oxygen and CO <sub>2</sub> sensors ( [[#Bourlès--2019|Bourlès et al., 2019]] ; [[#Hermes--2019|Hermes et al., 2019]] ; [[#Smith--2019|]] [[#Smith--2019|]] [[#Smith--2019|Smith et al., 2019]] ).

A decade of observations of sea-surface salinity is now available via the SMOS and SMAP satellite retrievals, providing continuous and global monitoring of surface salinity in the open ocean and coastal areas for the first time (Section 9.2.2.2; [[#Vinogradova--2019|Vinogradova et al., 2019]] ; [[#Reul--2020|Reul et al., 2020]] ).

The global network of tide gauges, complemented by a growing number of satellite-based altimetry datasets, allows for more robust estimates of global and regional sea level rise (Sections 2.3.3.3 and 9.6.1.3). Incorporating vertical land motion derived from the Global Positioning System (GPS), the comparison with tide gauges has allowed the correction of a drift in satellite altimetry series over the period 1993–1999 ( [[#Watson--2015|Watson et al., 2015]] ; [[#Chen--2017|Chen et al., 2017]] ), thus improving our knowledge of the recent acceleration of sea level rise (Chapter 2, [[IPCC:Wg1:Chapter:Chapter-2#2.3.3.3|Section 2.3.3.3]] ). These datasets, combined with Argo and observations of the cryosphere, allow a consistent closure of the global mean sea level budget (Cross-Chapter Box 9.1; [[#WCRP%20Global%20Sea%20Level%20Budget%20Group--2018|WCRP Global Sea Level Budget Group, 2018]] ).

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