Recent water mass changes reveal mechanisms of ocean warming

AbstractOver 90% of the build up of additional heat in the earth system over recent decades is contained in the ocean. Since 2006 new observational programs have revealed heterogeneous patterns of ocean heat content change. It is unclear how much of this heterogeneity is due to heat being added to and mixed within the ocean leading to material changes in water mass properties or due to changes in circulation which redistribute existing water masses. Here we present a novel diagnosis of the ‘material’ and ‘redistributed’ contributions to regional heat content change between 2006 and 2017 based on a new Minimum Transformation Method informed by both water mass transformation and optimal transportation theory. We show that material warming has large spatial coherence. The material change tends to be smaller than the redistributed change at any geographical location, however it sums globally to the net warming of the ocean, while the redistributed component sums, by design, to zero. Material warming is robust over the time period of this analysis, whereas the redistributed signal only emerges from the variability in a few regions. In the North Atlantic, water mass changes indicate substantial material warming while redistribution cools the subpolar region due to a slowdown in the Meridional Overturning Circulation. Warming in the Southern Ocean is explained by material warming and by anomalous southward heat transport of 118 ± 50 TWdue to redistribution. Our results suggest near termprojections of ocean heat content change and therefore sea level change will hinge on understanding and predicting changes in ocean redistribution.

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On the North Atlantic Ocean Heat Content Change between 1955–70 and 1980–95

Journal of Climate ◽

10.1175/jcli-d-11-00187.1 ◽

2012 ◽

Vol 25 (10) ◽

pp. 3619-3628 ◽

Cited By ~ 14

Author(s):

Xiaoming Zhai ◽

Luke Sheldon

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Gulf Stream ◽

Large Scale ◽

North Atlantic Ocean ◽

Heat Content ◽

Ocean Heat Content ◽

The North ◽

Content Change ◽

The North Atlantic

Abstract The upper-ocean heat content of the North Atlantic has undergone significant changes over the last 50 years but the underlying physical mechanisms are not yet well understood. In the present study, the authors examine the North Atlantic ocean heat content change in the upper 700 m between the 1955–70 and 1980–95 periods. Consistent with previous studies, the large-scale pattern consists of warming of the tropics and subtropics and cooling of the subpolar ocean. However, this study finds that the most significant heat content change in the North Atlantic during these two time periods is the warming of the Gulf Stream region. Numerical experiments strongly suggest that this warming in the Gulf Stream region is largely driven by changes of the large-scale wind forcing. Furthermore, the increased ocean heat content in the Gulf Stream region appears to feedback on to the atmosphere, resulting in warmer surface air temperature and enhanced precipitation there.

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Estimating Oceanic Heat Content Change Using Isotherms

Journal of Climate ◽

10.1175/2009jcli2823.1 ◽

2009 ◽

Vol 22 (19) ◽

pp. 4953-4969 ◽

Cited By ~ 34

Author(s):

Matthew D. Palmer ◽

Keith Haines

Keyword(s):

North Atlantic ◽

Heat Content ◽

Volcanic Eruptions ◽

Ocean Heat Content ◽

Fall Rate ◽

The North ◽

Content Change ◽

Mean Temperature ◽

The Mean ◽

The North Atlantic

Abstract This paper presents a new analysis of ocean heat content changes over the last 50 yr using isotherms by calculating the mean temperature above the 14°C isotherm and the depth of the 14°C isotherm as separate variables. A new quantity called the “relative heat content” (“RHC”) is introduced, which represents the minimum local heat content change over time, relative to a fixed isotherm. It is shown how mean temperature and isotherm depth changes make separable and additive contributions to changes in RHC. Maps of RHC change between 1970 and 2000 show similar spatial patterns to a traditional fixed-depth ocean heat content change to 220 m. However, the separate contributions to RHC suggest a more spatially uniform contribution from warming above the isotherm, while isotherm depth changes show wind-driven signals, of which some are identifiable as being related to the North Atlantic Oscillation. The time series show that the warming contribution to RHC dominates the global trend, while the depth contribution only dominates on the basin scale in the North Atlantic. The RHC shows minima associated with the major volcanic eruptions (particularly in the Indian Ocean), and these are entirely contributed by mean temperature changes rather than isotherm depth changes. The depth change contributions to RHC are strongly affected by the recently reported XBT fall-rate bias, whereas the mean temperature contributions are not. Therefore, only the isotherm depth change contributions to RHC will need to be reassessed as fall-rate-corrected data become available.

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Ocean Cooling Pattern at the Last Glacial Maximum

Advances in Meteorology ◽

10.1155/2012/213743 ◽

2012 ◽

Vol 2012 ◽

pp. 1-8 ◽

Cited By ~ 4

Author(s):

Kelin Zhuang ◽

John R. Giardino

Keyword(s):

Last Glacial Maximum ◽

Heat Content ◽

Glacial Maximum ◽

Meridional Overturning Circulation ◽

Last Glacial ◽

The North ◽

Content Change ◽

Cooling Pattern ◽

The Last Glacial Maximum ◽

The Last Glacial

Ocean temperature and ocean heat content change are analyzed based on four PMIP3 model results at the Last Glacial Maximum relative to the prehistorical run. Ocean cooling mostly occurs in the upper 1000 m depth and varies spatially in the tropical and temperate zones. The Atlantic Ocean experiences greater cooling than the rest of the ocean basins. Ocean cooling is closely related to the weakening of meridional overturning circulation and enhanced intrusion of Antarctic Bottom Water into the North Atlantic.

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Latest Miocene restriction of the Mediterranean Outflow Water: a perspective from the Gulf of Cádiz

Geo-Marine Letters ◽

10.1007/s00367-021-00693-9 ◽

2021 ◽

Vol 41 (2) ◽

Author(s):

Zhi Lin Ng ◽

F. Javier Hernández-Molina ◽

Débora Duarte ◽

Francisco J. Sierro ◽

Santiago Ledesma ◽

...

Keyword(s):

Mass Exchange ◽

Water Mass ◽

Atlantic Water ◽

Meridional Overturning Circulation ◽

Gulf Of Cadiz ◽

Mediterranean Outflow Water ◽

Gulf Of Cádiz ◽

Mediterranean Outflow ◽

The Mediterranean ◽

Water Mass Exchange

AbstractThe Mediterranean-Atlantic water mass exchange provides the ideal setting for deciphering the role of gateway evolution in ocean circulation. However, the dynamics of Mediterranean Outflow Water (MOW) during the closure of the Late Miocene Mediterranean-Atlantic gateways are poorly understood. Here, we define the sedimentary evolution of Neogene basins from the Gulf of Cádiz to the West Iberian margin to investigate MOW circulation during the latest Miocene. Seismic interpretation highlights a middle to upper Messinian seismic unit of transparent facies, whose base predates the onset of the Messinian salinity crisis (MSC). Its facies and distribution imply a predominantly hemipelagic environment along the Atlantic margins, suggesting an absence or intermittence of MOW preceding evaporite precipitation in the Mediterranean, simultaneous to progressive gateway restriction. The removal of MOW from the Mediterranean-Atlantic water mass exchange reorganized the Atlantic water masses and is correlated to a severe weakening of the Atlantic Meridional Overturning Circulation (AMOC) and a period of further cooling in the North Atlantic during the latest Miocene.

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On Anomalous Ocean Heat Transport toward the Arctic and Associated Climate Predictability

Journal of Climate ◽

10.1175/jcli-d-15-0448.1 ◽

2016 ◽

Vol 29 (2) ◽

pp. 689-704 ◽

Cited By ~ 39

Author(s):

Marius Årthun ◽

Tor Eldevik

Keyword(s):

Heat Transport ◽

Air Temperature ◽

Time Scale ◽

Heat Content ◽

Surface Air Temperature ◽

Meridional Overturning Circulation ◽

Ocean Heat Content ◽

The Arctic ◽

Ocean Heat Transport ◽

Climate Predictability

Abstract A potential for climate predictability is rooted in anomalous ocean heat transport and its consequent influence on the atmosphere above. Here the propagation, drivers, and atmospheric impact of heat anomalies within the northernmost limb of the Atlantic meridional overturning circulation are assessed using a multicentury climate model simulation. Consistent with observation-based inferences, simulated heat anomalies propagate from the eastern subpolar North Atlantic into and through the Nordic seas. The dominant time scale of associated climate variability in the northern seas is 14 years, including that of observed sea surface temperature and modeled ocean heat content, air–sea heat flux, and surface air temperature. A heat budget analysis reveals that simulated ocean heat content anomalies are driven by poleward ocean heat transport, primarily related to variable volume transport. The ocean’s influence on the atmosphere, and hence regional climate, is manifested in the model by anomalous ocean heat convergence driving subsequent changes in surface heat fluxes and surface air temperature. The documented northward propagation of thermohaline anomalies in the northern seas and their consequent imprint on the regional atmosphere—including the existence of a common decadal time scale of variability—detail a key aspect of eventual climate predictability.

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Surface predictor of overturning circulation and heat content change in the subpolar North Atlantic

Ocean Science ◽

10.5194/os-15-809-2019 ◽

2019 ◽

Vol 15 (3) ◽

pp. 809-817 ◽

Cited By ~ 9

Author(s):

Damien G. Desbruyères ◽

Herlé Mercier ◽

Guillaume Maze ◽

Nathalie Daniault

Keyword(s):

North Atlantic ◽

Spatial Scales ◽

Low Frequency ◽

Heat Content ◽

Climatic Conditions ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

The North ◽

Wide Range ◽

Key Aspects

Abstract. The Atlantic Meridional Overturning Circulation (AMOC) impacts ocean and atmosphere temperatures on a wide range of temporal and spatial scales. Here we use observational datasets to validate model-based inferences on the usefulness of thermodynamics theory in reconstructing AMOC variability at low frequency, and further build on this reconstruction to provide prediction of the near-future (2019–2022) North Atlantic state. An easily observed surface quantity – the rate of warm to cold transformation of water masses at high latitudes – is found to lead the observed AMOC at 45∘ N by 5–6 years and to drive its 1993–2010 decline and its ongoing recovery, with suggestive prediction of extreme intensities for the early 2020s. We further demonstrate that AMOC variability drove a bi-decadal warming-to-cooling reversal in the subpolar North Atlantic before triggering a recent return to warming conditions that should prevail at least until 2021. Overall, this mechanistic approach of AMOC variability and its impact on ocean temperature brings new key aspects for understanding and predicting climatic conditions in the North Atlantic and beyond.

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Water mass distributions and transports for the 2014 GEOVIDE cruise in the North Atlantic

Biogeosciences ◽

10.5194/bg-15-2075-2018 ◽

2018 ◽

Vol 15 (7) ◽

pp. 2075-2090 ◽

Cited By ~ 21

Author(s):

Maribel I. García-Ibáñez ◽

Fiz F. Pérez ◽

Pascale Lherminier ◽

Patricia Zunino ◽

Herlé Mercier ◽

...

Keyword(s):

North Atlantic ◽

Water Mass ◽

Water Levels ◽

Water Masses ◽

Meridional Overturning Circulation ◽

Labrador Sea ◽

Intermediate Water ◽

North East ◽

The North ◽

The North Atlantic

Abstract. We present the distribution of water masses along the GEOTRACES-GA01 section during the GEOVIDE cruise, which crossed the subpolar North Atlantic Ocean and the Labrador Sea in the summer of 2014. The water mass structure resulting from an extended optimum multiparameter (eOMP) analysis provides the framework for interpreting the observed distributions of trace elements and their isotopes. Central Waters and Subpolar Mode Waters (SPMW) dominated the upper part of the GEOTRACES-GA01 section. At intermediate depths, the dominant water mass was Labrador Sea Water, while the deep parts of the section were filled by Iceland–Scotland Overflow Water (ISOW) and North-East Atlantic Deep Water. We also evaluate the water mass volume transports across the 2014 OVIDE line (Portugal to Greenland section) by combining the water mass fractions resulting from the eOMP analysis with the absolute geostrophic velocity field estimated through a box inverse model. This allowed us to assess the relative contribution of each water mass to the transport across the section. Finally, we discuss the changes in the distribution and transport of water masses between the 2014 OVIDE line and the 2002–2010 mean state. At the upper and intermediate water levels, colder end-members of the water masses replaced the warmer ones in 2014 with respect to 2002–2010, in agreement with the long-term cooling of the North Atlantic Subpolar Gyre that started in the mid-2000s. Below 2000 dbar, ISOW increased its contribution in 2014 with respect to 2002–2010, with the increase being consistent with other estimates of ISOW transports along 58–59° N. We also observed an increase in SPMW in the East Greenland Irminger Current in 2014 with respect to 2002–2010, which supports the recent deep convection events in the Irminger Sea. From the assessment of the relative water mass contribution to the Atlantic Meridional Overturning Circulation (AMOC) across the OVIDE line, we conclude that the larger AMOC intensity in 2014 compared to the 2002–2010 mean was related to both the increase in the northward transport of Central Waters in the AMOC upper limb and to the increase in the southward flow of Irminger Basin SPMW and ISOW in the AMOC lower limb.

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Heat content in the Norwegian Sea, 1995–2010

ICES Journal of Marine Science ◽

10.1093/icesjms/fss026 ◽

2012 ◽

Vol 69 (5) ◽

pp. 826-832 ◽

Cited By ~ 26

Author(s):

Øystein Skagseth ◽

Kjell Arne Mork

Keyword(s):

Heat Content ◽

Atlantic Water ◽

Heat Fluxes ◽

Gradual Transition ◽

Absolute Maximum ◽

Nordic Seas ◽

Norwegian Sea ◽

Ocean Climate ◽

The North ◽

Spatio Temporal

Abstract Skagseth, Ø., and Mork, K. A. 2012. Heat content in the Norwegian Sea, 1995–2010. – ICES Journal of Marine Science, 69: 826–832. Spatio-temporal hydrographic data from the Nordic Seas during spring over the period 1995–2010 were investigated in terms of the relative heat content (RHC) above the density surface σt = 27.9, chosen to capture the changes in Atlantic water (AW). Focusing on the Atlantic (eastern) domain of the Nordic Seas, negative anomalies dominated the early part of the series. There was then a gradual transition towards an absolute maximum in 2003/2004, followed by a small reduction with positive values for the period ending in 2010. The maps clearly reveal the events of propagating signals. The variability is regionally comparable, but the persistence on a year-to-year basis is higher in the Lofoten Basin than in the Norwegian Basin. Compared with other studies, in this study, the estimated trend in the RHC of the Nordic Seas was larger than for the global mean and the North Atlantic. The warming of the Nordic Seas derives mainly from the advection of warmer inflowing AW and less from changes in local air–sea heat fluxes. The importance of advection suggests that the variability of the Norwegian Sea's ocean climate can, to a large extent, be predicted based on the observed hydrographic conditions.

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Are Cryosphere-Driven Feedbacks a Requisite for Abrupt Climate Events?

10.5194/egusphere-egu2020-19225 ◽

2020 ◽

Author(s):

Dakota Holmes ◽

Audrey Morley

Keyword(s):

Ocean Circulation ◽

Geographical Location ◽

Greenland Ice Sheet ◽

Meridional Overturning Circulation ◽

Grain Size Analysis ◽

Size Analysis ◽

North Atlantic Current ◽

Climate Change Research ◽

The North ◽

Climate Events

<p>Abrupt climate events are generally believed to be characteristic of glacial (intermediate-to-large cryosphere) climate states, requiring either sizeable ice-sheets or large freshwater pulses to act as triggers for abrupt climate changes to occur. Amplification occurs when these triggers bear upon the Atlantic Meridional Overturning Circulation (AMOC). However, the focus on glacial climate states in abrupt climate change research has led to an underrepresentation of research into interglacial periods. It thus remains unclear whether high-magnitude climate variability requires large cryosphere-driven feedbacks or whether it can also occur under low ice conditions. Here we present a high resolution analysis of surface and deep water components of the AMOC spanning the transition from Marine Isotope Stage (MIS) 19c to 19a to test if orbital boundary conditions similar to our current Holocene can accommodate abrupt climate events. Sediment core DSDP 610B (53&#176;13.297N, 18&#176;53.213W), located approximately 700-km west of Ireland, was specifically chosen due to its high sedimentation rate during interglacial periods, excellent core recovery over the Quaternary and its unique geographical location. Above the core site, the dominant oceanographic feature is the North Atlantic Current and at 2417-m water depth, 610B is influenced by Wyville Thomson Overflow Water flowing southwards. A multiproxy approach including paired grain size analysis, planktic foraminifer assemblage counts, and ice-rafted debris counts within the same samples allows us to resolve the timing between both surface and bottom components of the AMOC and their response to abrupt climate events during MIS-19 in the eastern subpolar gyre. This study is societally relevant as future freshwater inputs from a melting Greenland ice sheet may impact ocean circulation, potentially causing shifts in climate for many European countries.</p>

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