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2018
Cazenave, A, Meyssignac B, Ablain M, Balmaseda M, Bamber J, Barletta V, Beckley B, Benveniste J, Berthier E, Blazquez A, Boyer T, Caceres D, Chambers D, Champollion N, Chao B, Chen JL, Cheng LJ, Church JA, Chuter S, Cogley JG, Dangendorf S, Desbruyeres D, Doll P, Domingues C, Falk U, Famiglietti J, Fenoglio-Marc L, Forsberg R, Galassi G, Gardner A, Groh A, Hamlington B, Hogg A, Horwath M, Humphrey V, Husson L, Ishii M, Jaeggi A, Jevrejeva S, Johnson G, Kolodziejczyk N, Kusche J, Lambeck K, Landerer F, Leclercq P, Legresy B, Leuliette E, Llovel W, Longuevergne L, Loomis BD, Luthcke SB, Marcos M, Marzeion B, Merchant C, Merrifield M, Milne G, Mitchum G, Mohajerani Y, Monier M, Monselesan D, Nerem S, Palanisamy H, Paul F, Perez B, Piecuch CG, Ponte RM, Purkey SG, Reager JT, Rietbroek R, Rignot E, Riva R, Roemmich DH, Sorensen LS, Sasgen I, Schrama EJO, Seneviratne SI, Shum CK, Spada G, Stammer D, van de Wal R, Velicogna I, von Schuckmann K, Wada Y, Wang YG, Watson C, Wiese D, Wijffels S, Westaway R, Woppelmann G, Wouters B, Grp WGSLB.  2018.  Global sea-level budget 1993-present. Earth System Science Data. 10:1551-1590.   10.5194/essd-10-1551-2018   AbstractWebsite

Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g.,acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled "Regional Sea Level and Coastal Impacts", an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017-2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 +/- 0.3mm yr(-1) and acceleration of 0.1 mm yr(-2) over 1993-present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42%, 21%, 15% and 8% to the global mean sea level over the 1993-present period. We also study the sea-level budget over 2005-present, using GRACE-based ocean mass estimates instead of the sum of individual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3 mm yr(-1) (1 sigma). Substantial uncertainty remains for the land water storage component, as shown when examining individual mass contributions to sea level.

Durack, PJ, Gleckler PJ, Purkey SG, Johnson GC, Lyman JM, Boyer TP.  2018.  Ocean warming: From the surface to the deep in observations and models. Oceanography. 31:41-51.   10.5670/oceanog.2018.227   AbstractWebsite

The ocean is the primary heat sink of the global climate system. Since 1971, it has been responsible for storing more than 90% of the excess heat added to the Earth system by anthropogenic greenhouse-gas emissions. Adding this heat to the ocean contributes substantially to sea level rise and affects vital marine ecosystems. Considering the global ocean's large role in ongoing climate variability and change, it is a good place to focus in order to understand what observed changes have occurred to date and, by using models, what future changes might arise under continued anthropogenic forcing of the climate system. While sparse measurement coverage leads to enhanced uncertainties with long-term historical estimates of change, modern measurements are beginning to provide the clearest picture yet of ongoing global ocean change. Observations show that the ocean is warming from the near-surface through to the abyss, a conclusion that is strengthened with each new analysis. In this assessment, we revisit observation- and model-based estimates of ocean warming from the industrial era to the present and show a consistent, full-depth pattern of change over the observed record that is likely to continue at an ever-increasing pace if effective actions to reduce greenhouse-gas emissions are not taken.

2012
Purkey, SG, Johnson GC.  2012.  Global Contraction of Antarctic Bottom Water between the 1980s and 2000s. Journal of Climate. 25:5830-5844.   10.1175/JCLI-D-11-00612.1   AbstractWebsite

A statistically significant reduction in Antarctic Bottom Water (AABW) volume is quantified between the 1980s and 2000s within the Southern Ocean and along the bottom-most, southern branches of the meridional overturning circulation (MOC). AABW has warmed globally during that time, contributing roughly 10% of the recent total ocean heat uptake. This warming implies a global-scale contraction of AABW. Rates of change in AABW-related circulation are estimated in most of the world's deep-ocean basins by finding average rates of volume loss or gain below cold, deep potential temperature (theta) surfaces using all available repeated hydrographic sections. The Southern Ocean is losing water below theta = 0 degrees C at a rate of -8.2 (+/- 2.6) 3 10(6) m(3) s (1). This bottom water contraction causes a descent of potential isotherms throughout much of the water column until a near-surface recovery, apparently through a southward surge of Circumpolar Deep Water from the north. To the north, smaller losses of bottom waters are seen along three of the four main northward outflow routes of AABW. Volume and heat budgets below deep, cold theta surfaces within the Brazil and Pacific basins are not in steady state. The observed changes in volume and heat of the coldest waters within these basins could be accounted for by small decreases to the volume transport or small increases to theta of their inflows, or fractional increases in deep mixing. The budget calculations and global contraction pattern are consistent with a global-scale slowdown of the bottom, southern limb of the MOC.