North Atlantic Ocean Internal Decadal Variability: Role of the Mean State and Ocean‐Atmosphere Coupling

Abstract The rapid warming in the mid-1990s in the North Atlantic Ocean is investigated by means of an eddy-permitting ocean reanalysis. Both the mean state and variability, including the mid-1990s warming event, are well captured by the reanalysis. An ocean heat budget applied to the subpolar gyre (SPG) region (50°–66°N, 60°–10°W) shows that the 1995–99 rapid warming is primarily dictated by changes in the heat transport convergence term while the surface heat fluxes appear to play a minor role. The mean negative temperature increment suggests a warm bias in the model and data assimilation corrects the mean state of the model, but it is not crucial to reconstruct the time variability of the upper-ocean temperature. The decomposition of the heat transport across the southern edge of the SPG into time-mean and time-varying components shows that the SPG warming is mainly associated with both the anomalous advection of mean temperature and the mean advection of temperature anomalies across the 50°N zonal section. The relative contributions of the Atlantic meridional overturning circulation (AMOC) and gyre circulation to the heat transport are also analyzed. It is shown that both the overturning and gyre components are relevant to the mid-1990s warming. In particular, the fast adjustment of the barotropic circulation response to the NAO drives the anomalous transport of mean temperature at the subtropical/subpolar boundary, while the slowly evolving AMOC feeds the large-scale advection of thermal anomalies across 50°N. The persistently positive phase of the NAO during the years prior to the rapid warming likely favored the cross-gyre heat transfer and the following SPG warming.

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The role of Atlantic Ocean-atmosphere coupling in affecting North Atlantic oscillation variability

The North Atlantic Oscillation: Climatic Significance and Environmental Impact - Geophysical Monograph Series ◽

10.1029/134gm07 ◽

2003 ◽

pp. 147-172 ◽

Cited By ~ 41

Author(s):

Arnaud Czaja ◽

Andrew W. Robertson ◽

Thierry Huck

Keyword(s):

Atlantic Ocean ◽

North Atlantic Oscillation ◽

North Atlantic ◽

Ocean Atmosphere

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Acceleration of ocean warming, salinification, deoxygenation and acidification in the surface subtropical North Atlantic Ocean

Communications Earth & Environment ◽

10.1038/s43247-020-00030-5 ◽

2020 ◽

Vol 1 (1) ◽

Author(s):

Nicholas Robert Bates ◽

Rodney J. Johnson

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Decadal Variability ◽

North Atlantic Ocean ◽

Surface Warming ◽

Time Series Study ◽

Physical Conditions ◽

The Past ◽

Recent Warming ◽

Series Study

Abstract Ocean chemical and physical conditions are changing. Here we show decadal variability and recent acceleration of surface warming, salinification, deoxygenation, carbon dioxide (CO2) and acidification in the subtropical North Atlantic Ocean (Bermuda Atlantic Time-series Study site; 1980s to present). Surface temperatures and salinity exhibited interdecadal variability, increased by ~0.85 °C (with recent warming of 1.2 °C) and 0.12, respectively, while dissolved oxygen levels decreased by ~8% (~2% per decade). Concurrently, seawater DIC, fCO2 (fugacity of CO2) and anthropogenic CO2 increased by ~8%, 22%, and 72% respectively. The winter versus summer fCO2 difference increased by 4 to 8 µatm decade−1 due to seasonally divergent thermal and alkalinity changes. Ocean pH declined by 0.07 (~17% increase in acidity) and other acidification indicators by ~10%. Over the past nearly forty years, the highest increase in ocean CO2 and ocean acidification occurred during decades of weakest atmospheric CO2 growth and vice versa.

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Linking North Atlantic ocean-atmosphere teleconnection patterns and hydrogeological responses in temperate groundwater systems

Hydrological Processes ◽

10.1002/hyp.7466 ◽

2009 ◽

Vol 23 (21) ◽

pp. 3123-3126 ◽

Cited By ~ 15

Author(s):

I. P. Holman ◽

M. Rivas-Casado ◽

N. J. K. Howden ◽

J. P. Bloomfield ◽

A. T. Williams

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Teleconnection Patterns ◽

Ocean Atmosphere ◽

Groundwater Systems

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Predictability and Decadal Variability of the North Atlantic Ocean State Evaluated from a Realistic Ocean Model

Journal of Climate ◽

10.1175/jcli-d-16-0323.1 ◽

2017 ◽

Vol 30 (2) ◽

pp. 477-498 ◽

Cited By ~ 6

Author(s):

Florian Sévellec ◽

Alexey V. Fedorov

Keyword(s):

Atlantic Ocean ◽

Surface Temperature ◽

Sea Surface Temperature ◽

North Atlantic ◽

Decadal Variability ◽

North Atlantic Ocean ◽

Meridional Overturning Circulation ◽

Sea Surface ◽

The North ◽

The North Atlantic

This study investigates the excitation of decadal variability and predictability of the ocean climate state in the North Atlantic. Specifically, initial linear optimal perturbations (LOPs) in temperature and salinity that vary with depth, longitude, and latitude are computed, and the maximum impact on the ocean of these perturbations is evaluated in a realistic ocean general circulation model. The computations of the LOPs involve a maximization procedure based on Lagrange multipliers in a nonautonomous context. To assess the impact of these perturbations four different measures of the North Atlantic Ocean state are used: meridional volume and heat transports (MVT and MHT) and spatially averaged sea surface temperature (SST) and ocean heat content (OHC). It is shown that these metrics are dramatically different with regard to predictability. Whereas OHC and SST can be efficiently modified only by basin-scale anomalies, MVT and MHT are also strongly affected by smaller-scale perturbations. This suggests that instantaneous or even annual-mean values of MVT and MHT are less predictable than SST and OHC. Only when averaged over several decades do the former two metrics have predictability comparable to the latter two, which highlights the need for long-term observations of the Atlantic meridional overturning circulation in order to accumulate climatically relevant data. This study also suggests that initial errors in ocean temperature of a few millikelvins, encompassing both the upper and deep ocean, can lead to ~0.1-K errors in the predictions of North Atlantic sea surface temperature on interannual time scales. This transient error growth peaks for SST and OHC after about 6 and 10 years, respectively, implying a potential predictability barrier.

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The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies

Science ◽

10.1126/science.1167404 ◽

2009 ◽

Vol 324 (5928) ◽

pp. 778-781 ◽

Cited By ~ 135

Author(s):

A. T. Evan ◽

D. J. Vimont ◽

A. K. Heidinger ◽

J. P. Kossin ◽

R. Bennartz

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Ocean Temperature ◽

Temperature Anomalies ◽

Tropical North Atlantic

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The mean state and variability of the North Atlantic circulation: a perspective from ocean reanalyses

10.5194/egusphere-egu2020-5575 ◽

2020 ◽

Author(s):

Laura Jackson ◽

Clotilde Dubois ◽

Gael Forget ◽

Keith Haines ◽

Matt Harrison ◽

...

Keyword(s):

North Atlantic ◽

Decadal Variability ◽

Heat Content ◽

Meridional Overturning Circulation ◽

Global Ocean ◽

The North ◽

Ocean Reanalyses ◽

The Mean ◽

The North Atlantic ◽

Mean State

The observational network around the North Atlantic has improved significantly over the last few decades with the advent of Argo and satellite observations, and the more recent efforts to monitor the Atlantic Meridional Overturning Circulation (AMOC) using arrays such as RAPID and OSNAP. These have shown decadal timescale changes across the North Atlantic including in heat content, heat transport and the circulation.&#160;However there are still significant gaps in the observational coverage, and significant uncertainties around some observational products. Ocean reanalyses integrate the observations with a dynamically consistent ocean model and are potentially tools that can be used to understand the observed changes. However the suitability of the reanalyses for the task must also be assessed. We use an ensemble of global ocean reanalyses in comparison with observations in order to examine the mean state and interannual-decadal variability of the North Atlantic ocean since 1993. We assess how well the reanalyses are able to capture different processes and whether any understanding can be inferred. In particular we look at ocean heat content, transports, the AMOC and gyre strengths, water masses and convection.&#160;&#160;

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Coupled Modes of North Atlantic Ocean‐Atmosphere Variability and the Onset of the Little Ice Age

Geophysical Research Letters ◽

10.1029/2019gl084350 ◽

2019 ◽

Vol 46 (21) ◽

pp. 12417-12426 ◽

Cited By ~ 2

Author(s):

Kevin J. Anchukaitis ◽

Edward R. Cook ◽

Benjamin I. Cook ◽

Jessie Pearl ◽

Rosanne D'Arrigo ◽

...

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Little Ice Age ◽

North Atlantic Ocean ◽

Ice Age ◽

Coupled Modes ◽

Ocean Atmosphere

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Analyzing the Influence of the North Atlantic Ocean Variability on the Atlantic Meridional Mode on Decadal Time Scales

Atmosphere ◽

10.3390/atmos11010003 ◽

2019 ◽

Vol 11 (1) ◽

pp. 3

Author(s):

Sandro F. Veiga ◽

Emanuel Giarolla ◽

Paulo Nobre ◽

Carlos A. Nobre

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Decadal Variability ◽

North Atlantic Ocean ◽

Heat Content ◽

Ocean Heat Content ◽

Causality Analysis ◽

Ocean Variability ◽

The North ◽

The North Atlantic

Important features of the Atlantic meridional mode (AMM) are not fully understood. We still do not know what determines its dominant decadal variability or the complex physical processes that sustain it. Using reanalysis datasets, we investigated the influence of the North Atlantic Ocean variability on the dominant decadal periodicity that characterizes the AMM. Statistical analyses demonstrated that the correlation between the sea surface temperature decadal variability in the Atlantic Ocean and the AMM time series characterizes the Atlantic multidecadal oscillation (AMO). This corroborates previous studies that demonstrated that the AMO precedes the AMM. A causal inference with a newly developed rigorous and quantitative causality analysis indicates that the AMO causes the AMM. To further understand the influence of the subsurface ocean on the AMM, the relationship between the ocean heat content (0–300 m) decadal variability and AMM was analyzed. The results show that although there is a significant zero-lag correlation between the ocean heat content in some regions of the North Atlantic (south of Greenland and in the eastern part of the North Atlantic) and the AMM, their cause-effect relationship on decadal time scales is unlikely. By correlating the AMO with the ocean heat content (0–300 m) decadal variability, the former precedes the latter; however, the causality analysis shows that the ocean heat content variability drives the AMO, corroborating several studies that point out the dominant role of the ocean heat transport convergence on AMO.

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Green Sahara Megaperiods during the Pliocene: What was the role of North Atlantic Ocean temperature?

10.5194/egusphere-egu2020-20327 ◽

2020 ◽

Author(s):

Paul Wilson ◽

Amy Jewell ◽

Anya Crocker ◽

Solana Buchanan ◽

Bryce Mitsunaga ◽

...

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Saharan Dust ◽

The North ◽

Sst Variability ◽

Scan Data ◽

Sahel Region ◽

Strong Control

The Sahel region is one of the most vulnerable regions on Earth to anthropogenically-driven climate change, but also one of the least equipped to deal with the consequences. Predictions of precipitation levels over the forthcoming centuries diverge, not only in magnitude, but also in the sign of change. One key aspect of this uncertainty comes from the role of Atlantic Ocean sea surface temperatures (SST), which are known to exert a strong control over precipitation in the Sahel and are implicated in both the major drought of the late 20th century and extreme droughts associated with the Heinrich events of the last glacial. To better understand how Sahelian hydroclimate may respond to SST variability in a warmer world, we turn to the Pliocene epoch, when atmospheric CO2 levels were comparable to present.&#160;We studied sediments from Ocean Drilling Project Site 659, which is situated in the subtropical North Atlantic beneath the major modern summer Saharan dust plume. Our new dust accumulation rates and X-ray fluorescence core scan data indicate that there were major shifts between highly arid conditions and humid intervals with vegetated or &#8220;Green Sahara&#8221; conditions over much of northern Africa, driven by both solar insolation and glacial-interglacial variability. We also report three unusually long Plio-Pliocene humid intervals (each lasting ca. 100 kyr) characterised by very low dust emissions, that we term &#8220;Green Sahara Megaperiods (GSMPs)&#8221;. All three of these GSMPs occur at times when insolation variability was weak, resulting in values close to the long-term mean. This observation strongly suggests that factors other than insolation drove the sustained humidity of GSMPs. We present paired alkenone SST estimates and multi-species planktonic foramaniferal isotope records from 3.5&#8211;2.3 Myr ago to explore the extent to which the GSMPs were accompanied by intervals of extended warmth in the surface waters of the North Atlantic Ocean.

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