Decomposing oceanic temperature and salinity change using ocean carbon change

Abstract. As the planet warms due to the accumulation of anthropogenic CO2 in the atmosphere, the global ocean uptake of heat can largely be described as a linear function of anthropogenic CO2 uptake. This relates the oceans mitigation of atmospheric warming and carbon sequestration, as well as its increasing heat content. Patterns of ocean salinity also change as the earth system warms due to hydrological cycle intensification and perturbations to air-sea freshwater fluxes. Local temperature and salinity change in the ocean may result from perturbed air-sea fluxes of heat and freshwater (excess temperature, salinity), or from variability resulting from reorganisation of the preindustrial temperature and salinity fields (redistributed temperature, salinity), which are largely due to circulation changes. Here, we present a novel method in which, by tracking the redistribution of preindustrial carbon, we may estimate the redistribution of temperature and salinity using only local spatial information. We demonstrate this technique by estimating the redistribution of heat and salinity in the NEMO OGCM coupled to the MEDUSA-2 Biogeochemistry model under a RCP8.5 scenario over 1860–2099. We find on the longest timescales, the patterns of excess heat and salinity storage are dominated by increases in excess heat and salinity in the Atlantic, and that excess salinity is generally negative in other basins, compensating for strong atmospheric transport of excess salinity to the Atlantic. We also find significant redistribution of heat away from the North Atlantic, and of salinity to the South Atlantic, consistent with AMOC slowdown. Temperature change at depth is accounted for predominately by redistributed, rather than excess heat, but the opposite is true for salinity, where the excess component accounts for the majority of changes at depth. Though by the end of the simulation excess heat is the largest contribution to density change and steric sea level rise, the storage of excess salinity greatly reduces variability in excess density, particularly in the Atlantic. Here, redistribution of the preindustrial heat and salinity fields also produce generally opposing changes in sea level, though patterns are less clear elsewhere. As expected, the regional strength of excess heat and salinity signal grows through the model run. In addition, the regional strength of the redistributed temperature and salinity signals also grow, indicating increasing circulation variability or systematic circulation change on at least the time scale of the model run.

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Consistency of the current global ocean observing systems from an Argo perspective

Ocean Science ◽

10.5194/os-10-547-2014 ◽

2014 ◽

Vol 10 (3) ◽

pp. 547-557 ◽

Cited By ~ 40

Author(s):

K. von Schuckmann ◽

J.-B. Sallée ◽

D. Chambers ◽

P.-Y. Le Traon ◽

C. Cabanes ◽

...

Keyword(s):

Sea Level ◽

Heat Content ◽

Deep Ocean ◽

Global Ocean ◽

Regional Variability ◽

Tropical Ocean ◽

Steric Sea Level ◽

Ocean Observing ◽

Ocean Observing Systems ◽

Observing Systems

Abstract. Variations in the world's ocean heat storage and its associated volume changes are a key factor to gauge global warming and to assess the earth's energy and sea level budget. Estimating global ocean heat content (GOHC) and global steric sea level (GSSL) with temperature/salinity data from the Argo network reveals a positive change of 0.5 ± 0.1 W m−2 (applied to the surface area of the ocean) and 0.5 ± 0.1 mm year−1 during the years 2005 to 2012, averaged between 60° S and 60° N and the 10–1500 m depth layer. In this study, we present an intercomparison of three global ocean observing systems: the Argo network, satellite gravimetry from GRACE and satellite altimetry. Their consistency is investigated from an Argo perspective at global and regional scales during the period 2005–2010. Although we can close the recent global ocean sea level budget within uncertainties, sampling inconsistencies need to be corrected for an accurate global budget due to systematic biases in GOHC and GSSL in the Tropical Ocean. Our findings show that the area around the Tropical Asian Archipelago (TAA) is important to closing the global sea level budget on interannual to decadal timescales, pointing out that the steric estimate from Argo is biased low, as the current mapping methods are insufficient to recover the steric signal in the TAA region. Both the large regional variability and the uncertainties in the current observing system prevent us from extracting indirect information regarding deep-ocean changes. This emphasizes the importance of continuing sustained effort in measuring the deep ocean from ship platforms and by beginning a much needed automated deep-Argo network.

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El Niño, La Niña, and the global sea level budget

Ocean Science ◽

10.5194/os-12-1165-2016 ◽

2016 ◽

Vol 12 (6) ◽

pp. 1165-1177 ◽

Cited By ~ 12

Author(s):

Christopher G. Piecuch ◽

Katherine J. Quinn

Keyword(s):

Sea Level ◽

El Niño ◽

Hydrological Cycle ◽

El Nino ◽

Southern Oscillation ◽

Heat Content ◽

Global Ocean ◽

Surface Warming ◽

Enso Events ◽

The Pacific

Abstract. Previous studies show that nonseasonal variations in global-mean sea level (GMSL) are significantly correlated with El Niño–Southern Oscillation (ENSO). However, it has remained unclear to what extent these ENSO-related GMSL fluctuations correspond to steric (i.e., density) or barystatic (mass) effects. Here we diagnose the GMSL budget for ENSO events observationally using data from profiling floats, satellite gravimetry, and radar altimetry during 2005–2015. Steric and barystatic effects make comparable contributions to the GMSL budget during ENSO, in contrast to previous interpretations based largely on hydrological models, which emphasize the barystatic component. The steric contributions reflect changes in global ocean heat content, centered on the Pacific. Distributions of ocean heat storage in the Pacific arise from a mix of diabatic and adiabatic effects. Results have implications for understanding the surface warming slowdown and demonstrate the usefulness of the Global Ocean Observing System for constraining Earth's hydrological cycle and radiation imbalance.

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El Niño, La Niña, and the global sea level budget

10.5194/os-2016-66 ◽

2016 ◽

Author(s):

Christopher G. Piecuch ◽

Katherine J. Quinn

Keyword(s):

Sea Level ◽

El Niño ◽

Hydrological Cycle ◽

El Nino ◽

Southern Oscillation ◽

Heat Content ◽

Global Ocean ◽

Surface Warming ◽

Enso Events ◽

The Pacific

Abstract. Previous studies show that nonseasonal variations in global-mean sea level (GMSL) are significantly correlated with El Niño-Southern Oscillation (ENSO). However, it has remained unclear to what extent these ENSO-related GMSL fluctuations correspond to steric (i.e., density) or barystatic (mass) effects. Here we diagnose the GMSL budget for ENSO events observationally using data from profiling floats, satellite gravimetry, and radar altimetry during 2005–2015. Steric and barystatic effects make comparable contributions to the GMSL budget during ENSO, in contrast to previous interpretations based largely on hydrological models, which emphasize the barystatic component. The steric contributions reflect changes in global ocean heat content, centered on the Pacific. Distributions of ocean heat storage in the Pacific arise from a mix of diabatic and adiabatic effects. Results have implications for understanding the surface warming slowdown and demonstrate the usefulness of the Global Ocean Observing System for constraining Earth's hydrological cycle and radiation imbalance.

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Transport of Excess Heat at 24.5°N

10.5194/egusphere-egu2020-22652 ◽

2020 ◽

Author(s):

Marie-José Messias ◽

Herlé Mercier

Keyword(s):

Heat Transport ◽

North Atlantic Ocean ◽

Heat Content ◽

Global Ocean ◽

Geochemical Tracers ◽

Excess Heat ◽

Future Evolution ◽

The North ◽

Source Regions ◽

Geographic Origins

<p>Repeated hydrographic surveys have allowed for the monitoring of the 24.5&#176;N trans-Atlantic transect of volume and heat transports &#160;since the middle of the last century. However, identifying the geographic origins and the temporal characteristics of full depth ocean heat content (OHC) anomalies is still at the frontier of&#160; global ocean warming research albeit it is critical to the &#160;understanding of &#160;the current warming of the ocean and its future evolution. To address this gap,&#160; we &#160;combine volume transports at 24.5&#176;N &#160;with an historical reconstruction of &#160;excess heat, which we define as the heat gained across the section since the year 1850 to &#160;present. The &#160;reconstruction is based on &#160;a maximum entropy approach &#160;that links the&#160;&#160;location and time of the last entry into the ocean of a series of transient and geochemical tracers to their full depth in situ measurements in the interior. Here, we apply it to tracers measured on the hydrographic sections at&#160;&#160;24.5&#176;N since 1992. This methodology is a step forward in exploring the coherence of the OHC distributions at 24.5&#176;N over time with the variability of the SST in &#160;the source regions and the role of the AMOC, all genuinely based on observations. We find that the AMOC ranges from 16 to 19 Sv, heat transport from 0.9 to 1.5 PW and excess heat transport from 19 to 31 TW. The excess heat is transported northward across 24.5&#176;N thus reinforcing the warming of the North Atlantic Ocean.</p>

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How Salty Is the Global Ocean: Weighting It All or Tasting It a Sip at a Time?

10.5194/gstm2020-12 ◽

2020 ◽

Author(s):

Rui Ponte ◽

Qiang Sun ◽

Chao Liu ◽

Xinfeng Liang

Keyword(s):

Sea Ice ◽

Sea Level ◽

Hydrological Cycle ◽

Global Ocean ◽

Data Quality Control ◽

Argo Data ◽

Terrestrial Water ◽

Control Procedures ◽

Global Mean Sea Level

<div class="page" title="Page 1"> <div class="section"> <div class="layoutArea"> <div class="column"> <p>Global ocean mean salinity <em>S </em>is a key indicator of the Earth's hydrological cycle and the exchanges of freshwater between the terrestrial water and ice reservoirs and the ocean. We explore two different ways of determining how salty the ocean is: (1) use in situ salinity measurements to taste the ocean a sip at a time and obtain a sample average; (2) use space gravimetry to weigh the whole ocean including sea-ice, and then separate sea-ice effects to infer changes in liquid freshwater content and thus <em>S</em>. Focusing on the 2005-2019 period, we assess monthly series of <em>S </em>derived from five different in situ gridded products, based mostly but not exclusively on Argo data, versus a series obtained from GRACE and GRACE Follow-On data and available sea ice mass estimates.</p> <p>There is little consistency in <em>S </em>series from the two methods for all time scales examined (seasonal, interannual, long-term trend). In situ series show larger variability, particularly at the longest scales, and are somewhat incoherent with the GRACE-derived series. In addition, there are wide spread differences among all the in situ <em>S </em>series, which denote their considerable sensitivity to choice of data, quality control procedures, and mapping methods. Results also suggest that in situ <em>S </em>values are prone to systematic biases, with most series showing increases after around 2014 that are equivalent to a drop in barystatic sea level of tens of centimeters! Estimates derived from GRACE are much smaller in magnitude and consistent with contributions of freshwater to the global mean sea level budgets, and they are thus more reliable than in situ-based <em>S </em>estimates. The existence of GRACE-derived estimates can serve as a consistency check on in situ measurements, revealing potential unknown biases and providing a way to cross-calibrate the latter data.</p> </div> </div> </div> </div>

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Dominance of the Southern Ocean in Anthropogenic Carbon and Heat Uptake in CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-14-00117.1 ◽

2015 ◽

Vol 28 (2) ◽

pp. 862-886 ◽

Cited By ~ 208

Author(s):

Thomas L. Frölicher ◽

Jorge L. Sarmiento ◽

David J. Paynter ◽

John P. Dunne ◽

John P. Krasting ◽

...

Keyword(s):

Southern Ocean ◽

Carbon Storage ◽

Heat Storage ◽

Global Ocean ◽

Cmip5 Models ◽

Co2 Uptake ◽

Anthropogenic Co2 ◽

Recent Climate ◽

Heat Uptake ◽

Anthropogenic Carbon

Abstract The authors assess the uptake, transport, and storage of oceanic anthropogenic carbon and heat over the period 1861–2005 in a new set of coupled carbon–climate Earth system models conducted for the fifth phase of the Coupled Model Intercomparison Project (CMIP5), with a particular focus on the Southern Ocean. Simulations show that the Southern Ocean south of 30°S, occupying 30% of global surface ocean area, accounts for 43% ± 3% (42 ± 5 Pg C) of anthropogenic CO2 and 75% ± 22% (23 ± 9 × 1022 J) of heat uptake by the ocean over the historical period. Northward transport out of the Southern Ocean is vigorous, reducing the storage to 33 ± 6 Pg anthropogenic carbon and 12 ± 7 × 1022 J heat in the region. The CMIP5 models, as a class, tend to underestimate the observation-based global anthropogenic carbon storage but simulate trends in global ocean heat storage over the last 50 years within uncertainties of observation-based estimates. CMIP5 models suggest global and Southern Ocean CO2 uptake have been largely unaffected by recent climate variability and change. Anthropogenic carbon and heat storage show a common broad-scale pattern of change, but ocean heat storage is more structured than ocean carbon storage. The results highlight the significance of the Southern Ocean for the global climate and as the region where models differ the most in representation of anthropogenic CO2 and, in particular, heat uptake.

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Changing Expendable Bathythermograph Fall Rates and Their Impact on Estimates of Thermosteric Sea Level Rise

Journal of Climate ◽

10.1175/2008jcli2290.1 ◽

2008 ◽

Vol 21 (21) ◽

pp. 5657-5672 ◽

Cited By ~ 166

Author(s):

Susan E. Wijffels ◽

Josh Willis ◽

Catia M. Domingues ◽

Paul Barker ◽

Neil J. White ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Decadal Variability ◽

Heat Content ◽

Time History ◽

Global Ocean ◽

Fall Rate ◽

Rate Minimum ◽

Fall Rates

Abstract A time-varying warm bias in the global XBT data archive is demonstrated to be largely due to changes in the fall rate of XBT probes likely associated with small manufacturing changes at the factory. Deep-reaching XBTs have a different fall rate history than shallow XBTs. Fall rates were fastest in the early 1970s, reached a minimum between 1975 and 1985, reached another maximum in the late 1980s and early 1990s, and have been declining since. Field XBT/CTD intercomparisons and a pseudoprofile technique based on satellite altimetry largely confirm this time history. A global correction is presented and applied to estimates of the thermosteric component of sea level rise. The XBT fall rate minimum from 1975 to 1985 appears as a 10-yr “warm period” in the global ocean in thermosteric sea level and heat content estimates using uncorrected data. Upon correction, the thermosteric sea level curve has reduced decadal variability and a larger, steadier long-term trend.

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C-GLORSv5: an improved multi-purpose global ocean eddy-permitting physical reanalysis

10.5194/essd-2016-38 ◽

2016 ◽

Author(s):

Andrea Storto ◽

Simona Masina

Keyword(s):

Bias Correction ◽

General Circulation ◽

Thermohaline Circulation ◽

Heat Content ◽

Global Ocean ◽

Observation Error ◽

Background Error ◽

Steric Sea Level ◽

Previous Version ◽

Correction Scheme

Abstract. Global ocean reanalyses combine in-situ and satellite ocean observations with a general circulation ocean model to estimate the time-evolving state of the ocean, and they represent a valuable tool for a variety of applications, ranging from climate monitoring and process studies to downstream applications, initialization of long-range forecasts and regional studies. The purpose of this paper is to document the recent upgrade of C-GLORS (version 5), a state-of-the-art ocean reanalysis produced at the Centro Euro-Mediterraneo per i Cambiamenti Climatici that covers the meteorological satellite era (1980–present) and it is being updated in delayed time mode. The reanalysis is run at eddy-permitting resolution (1/4 degree horizontal resolution and 50 vertical levels) and consists of a three-dimensional variational data assimilation system, a surface nudging and a bias correction scheme. With respect to the previous version (v4), C-GLORSv5 contains a number of improvements. In particular, background- and observation- error covariances have been retuned, allowing a flow-dependent inflation in the globally averaged background-error variance. An additional constraint on the sea-ice thickness was introduced, leading to a realistic ice volume evolution. Finally, the bias correction scheme and the initialization strategy were retuned. Results document that the new reanalysis outperforms the previous version, especially in representing the variability of global heat content and associated steric sea level, the upper ocean temperature and the thermohaline circulation. The dataset is available in NetCDF format at doi:10.1594/PANGAEA.857995.

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Forced and chaotic variability of interannual variability of regional sea level and its causes scale over 1993-2015

10.5194/egusphere-egu2020-5689 ◽

2020 ◽

Author(s):

Alice Carret ◽

William Llovel ◽

Thierry Penduff ◽

Jean-Marc Molines ◽

Benoît Meyssignac

Keyword(s):

Interannual Variability ◽

Sea Level ◽

Satellite Altimetry ◽

Global Ocean ◽

Western Boundary ◽

Western Boundary Currents ◽

Steric Sea Level ◽

Boundary Currents ◽

Ocean Variability ◽

Regional Sea Level

<p>Since the early 1990s, satellite altimetry has become the main observing system for continuously measuring the sea level variations with a near global coverage. Satellite altimetry has revealed a global mean sea level rise of 3.3 mm/yr since 1993 with large regional sea level variability that differs from the mean estimate. These measurements highlight complex structures especially for the western boundary currents or the Antarctic Circumpolar Current. A recent study shows that the chaotic ocean variability may mask atmospherically-forced regional sea level trends over 38% of the global ocean area from 1993 to 2015. The chaotic variability is large for the western boundary currents and in the Southern Ocean. The present study aims to complement this previous work in focusing on the interannual variability of regional sea level. A global &#188;&#176; ocean/sea-ice 50-member ensemble simulation is considered to disentangle the imprints of the atmospheric forcing and the chaotic ocean variability on the interannual variability of regional sea level over 1993-2015. We investigate the forced (i.e., ensemble mean) versus the chaotic variability (i.e., ensemble standard deviation) for the interannual variability of regional sea level and its causes (i.e., steric sea level and manometric sea level contribution). We complement our investigations by partitioning the steric component into thermosteric sea level (i.e., temperature change only) and halosteric sea level (i.e., salinity change only). One of the goals of the study is to highlight the hot spots region of large chaotic variability for regional sea level and its different components.</p>

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