scholarly journals Short communication. Carbon and nitrogen fluxes in the oceans: the contribution by zooplankton migrants to active transport in the North Atlantic during the Joint Global Ocean Flux Study

1999 ◽  
Vol 21 (9) ◽  
pp. 1799-1808 ◽  
Author(s):  
C Morales
Keyword(s):  
Active Transport ◽  
North Atlantic ◽  
Short Communication ◽  
Global Ocean ◽  
Carbon And Nitrogen ◽  
Nitrogen Fluxes ◽  
The North ◽  
The North Atlantic

The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation

2020 ◽  
Vol 33 (6) ◽  
pp. 2111-2130
Author(s):  
Woo Geun Cheon ◽  
Jong-Seong Kug
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
North Pacific ◽  
Global Ocean ◽  
The North ◽  
Westerly Winds ◽  
The North Atlantic ◽  
Global Ocean Circulation ◽  
The Antarctic ◽  
The North Pacific

AbstractIn the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circulation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven teleconnection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre). The North Atlantic Deep Water (NADW) formation is controlled by salt advected northward by the North Atlantic WBC.

scholarly journals Marine productivity response to Heinrich events: a model-data comparison

2012 ◽  
Vol 8 (5) ◽  
pp. 1581-1598 ◽  
Author(s):  
V. Mariotti ◽  
L. Bopp ◽  
A. Tagliabue ◽  
M. Kageyama ◽  
D. Swingedouw
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Heinrich Events ◽  
The North ◽  
Heinrich Event ◽  
The North Atlantic ◽  
Marine Productivity

Abstract. Marine sediments records suggest large changes in marine productivity during glacial periods, with abrupt variations especially during the Heinrich events. Here, we study the response of marine biogeochemistry to such an event by using a biogeochemical model of the global ocean (PISCES) coupled to an ocean-atmosphere general circulation model (IPSL-CM4). We conduct a 400-yr-long transient simulation under glacial climate conditions with a freshwater forcing of 0.1 Sv applied to the North Atlantic to mimic a Heinrich event, alongside a glacial control simulation. To evaluate our numerical results, we have compiled the available marine productivity records covering Heinrich events. We find that simulated primary productivity and organic carbon export decrease globally (by 16% for both) during a Heinrich event, albeit with large regional variations. In our experiments, the North Atlantic displays a significant decrease, whereas the Southern Ocean shows an increase, in agreement with paleo-productivity reconstructions. In the Equatorial Pacific, the model simulates an increase in organic matter export production but decreased biogenic silica export. This antagonistic behaviour results from changes in relative uptake of carbon and silicic acid by diatoms. Reasonable agreement between model and data for the large-scale response to Heinrich events gives confidence in models used to predict future centennial changes in marine production. In addition, our model allows us to investigate the mechanisms behind the observed changes in the response to Heinrich events.

Efficient carbon drawdown allows for a high future carbon uptake in the North Atlantic

2021 ◽  
Author(s):  
Nadine Goris ◽  
Jerry Tjiputra ◽  
Are Ohlsen ◽  
Jörg Schwinger ◽  
Siv Lauvset ◽  
...  
Keyword(s):  
North Atlantic ◽  
High Latitude ◽  
Deep Convection ◽  
Deep Ocean ◽  
Nutrient Supply ◽  
Global Ocean ◽  
Carbon Uptake ◽  
Model Ensemble ◽  
The North ◽  
The North Atlantic

<p>As one of the major carbon sinks in the global ocean, the North Atlantic is a key player in mediating and ameliorating the ongoing global warming. Projections of the North Atlantic carbon sink in a high-CO<sub>2</sub> future vary greatly among models, with some showing that a slowdown in carbon uptake has already begun and others predicting that this slowdown will not occur until nearly 2100.</p><p>Discrepancies among models largely originate because of differences in the efficiency of the high-latitude transport of carbon from the surface to the deep ocean. This transport occurs through biological production, deep convection and subsequent transport via the deep western boundary current. For an ensemble of 11 CMIP5-models, we studied the efficiency of this transport and identified two indicators of contemporary model behavior that are highly correlated with a model´s projected future carbon-uptake. The first indicator is the high latitude summer pCO<sub>2</sub><sup>sea</sup>-anomaly of a model, which is tightly linked to winter mixing and nutrient supply, but also to deep convection. The second indicator is the fraction of the anthropogenic carbon-inventory stored below 1000-m depth, indicating how efficient carbon is transported into the deep ocean. By comparing to the observational database, these indicators allow us to better constrain the model ensemble, and demonstrate that the models with more efficient surface to deep transport are best aligned with current observations. These models also show the largest future North Atlantic carbon uptake, which we then conclude is the more plausible future evolution. We further study if the high correlations between our contemporary indicators and a model´s future North Atlantic carbon uptake is also upheld for the next model generation, CMIP6. We hypothesize that this is the case and that our indicators can not only help us to constrain the CMIP6 model ensemble but also inform us about progress made between CMIP5 and CMIP6 in terms of North Atlantic carbon uptake, winter mixing, nutrient supply, deep convection and transport of carbon into the deep ocean.</p>

Variability of the Oceanic Mixed Layer, 1960–2004

2008 ◽  
Vol 21 (5) ◽  
pp. 1029-1047 ◽  
Author(s):  
James A. Carton ◽  
Semyon A. Grodsky ◽  
Hailong Liu
Keyword(s):  
Mixed Layer ◽  
North Atlantic ◽  
Southern Oscillation ◽  
Mixed Layer Depth ◽  
Global Ocean ◽  
Boreal Summer ◽  
Layer Depth ◽  
The North ◽  
The North Atlantic ◽  
Mixed Layers

Abstract A new monthly uniformly gridded analysis of mixed layer properties based on the World Ocean Atlas 2005 global ocean dataset is used to examine interannual and longer changes in mixed layer properties during the 45-yr period 1960–2004. The analysis reveals substantial variability in the winter–spring depth of the mixed layer in the subtropics and midlatitudes. In the North Pacific an empirical orthogonal function analysis shows a pattern of mixed layer depth variability peaking in the central subtropics. This pattern occurs coincident with intensification of local surface winds and may be responsible for the SST changes associated with the Pacific decadal oscillation. Years with deep winter–spring mixed layers coincide with years in which winter–spring SST is low. In the North Atlantic a pattern of winter–spring mixed layer depth variability occurs that is not so obviously connected to local changes in winds or SST, suggesting that other processes such as advection are more important. Interestingly, at decadal periods the winter–spring mixed layers of both basins show trends, deepening by 10–40 m over the 45-yr period of this analysis. The long-term mixed layer deepening is even stronger (50–100 m) in the North Atlantic subpolar gyre. At tropical latitudes the boreal winter mixed layer varies in phase with the Southern Oscillation index, deepening in the eastern Pacific and shallowing in the western Pacific and eastern Indian Oceans during El Niños. In boreal summer the mixed layer in the Arabian Sea region of the western Indian Ocean varies in response to changes in the strength of the southwest monsoon.

scholarly journals North Atlantic SST Anomalies and the Cold North European Weather Events of Winter 2009/10 and December 2010

2014 ◽  
Vol 142 (2) ◽  
pp. 922-932 ◽  
Author(s):  
Jian Buchan ◽  
Joël J.-M. Hirschi ◽  
Adam T. Blaker ◽  
Bablu Sinha
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Cold Weather ◽  
Global Ocean ◽  
Northern Europe ◽  
Significant Shift ◽  
The North ◽  
Extreme Cold ◽  
The North Atlantic ◽  
Sst Anomalies

Abstract Northern Europe experienced consecutive periods of extreme cold weather in the winter of 2009/10 and in late 2010. These periods were characterized by a tripole pattern in North Atlantic sea surface temperature (SST) anomalies and exceptionally negative phases of the North Atlantic Oscillation (NAO). A global ocean–atmosphere general circulation model (OAGCM) is used to investigate the ocean’s role in influencing North Atlantic and European climate. Observed SST anomalies are used to force the atmospheric model and the resultant changes in atmospheric conditions over northern Europe are examined. Different atmospheric responses occur in the winter of 2009/10 and the early winter of 2010. These experiments suggest that North Atlantic SST anomalies did not significantly affect the development of the negative NAO phase in the cold winter of 2009/10. However, in November and December 2010 the large-scale North Atlantic SST anomaly pattern leads to a significant shift in the atmospheric circulation over the North Atlantic toward a NAO negative phase. Therefore, these results indicate that SST anomalies in November/December 2010 were particularly conducive to the development of a negative NAO phase, which culminated in the extreme cold weather conditions experienced over northern Europe in December 2010.

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

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

<p>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. </p><p>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.<br>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. </p><p> </p>

scholarly journals NATO IN THE NEW STRATEGIC ENVIRONMENT: CYBER ATTACKS NOW COVERED BY ARTICLE 5 OF THE NORTH ATLANTIC TREATY

2014 ◽  
Vol 6 (2) ◽  
pp. 397-418 ◽  
Author(s):  
Grzegorz KOSTRZEWA-ZORBAS
Keyword(s):  
North Atlantic ◽  
The United States ◽  
Cyber Attacks ◽  
Global Ocean ◽  
Cyber Warfare ◽  
Security Environment ◽  
The North ◽  
The North Atlantic ◽  
Strategic Space ◽  
Article 5

The greatest change ever in the defence policy and military strategy of the North Atlantic Treaty Organisation occurred in 2014 in response to a series of major cyber attacks against NATO member states and partner states - Estonia in 2007, the United States and Georgia in 2008, and others in later years - and to a general transformation of the security environment in which cyberwar and other threats to cybersecurity gain rapidly in importance. At the 2014 Wales Summit, NATO recognised that cyber defence is part of its central task of collective defence and that Article 5 of the North Atlantic Treaty - ”The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all . . .” - can be invoked in the case of cyber attacks. This statement is the first and only expansion of the meaning of Article 5 and the first and only addition of a new type of warfare to the policy and strategy of NATO. After the change, the Alliance must face new challenges not less urgent and difficult than the old ones of kinetic warfare or weapons of mass destruction. This article addresses the broadest strategic context of the change. An analysis is made in the light of the global strategic thought and of the development of warfare through history. By entering the new strategic space of cyber warfare, NATO proves itself to be among the world’s most modern and advanced powers while, at the same time, it returns to the ancient - and lasting - tenet of strategy: information is not inferior to force. This way the Alliance moves away from Carl von Clausewitz and closer to Sun Zi. The recognition of cyberspace as a strategic space also corresponds to another influential idea in the heritage of strategy: the concept of the ”great common” the control of which is the key to the power over the world and over war and peace worldwide. Alfred Thayer Mahan considered the global ocean to be the ”great common” crossed by vital trade routes and by navies competing for superiority. Now cyberspace is as open, vital and fragile as the maritime space was in Mahan’s vision. Cyberwar also creates a promise and a temptation of a decisive strike - the first and last strike in a war - circumventing all military defences and paralysing the enemy country. It is a new version - less lethal or not, dependent on the tactics of cyber attacks in a cyber offensive - of the idea of strategic bombing and of the entire concept of air power, especially by its visionary Giulio Douhet, and then of nuclear strategy. Finally, the article provides two practical recommendations regarding the policy and structure of the North Atlantic Alliance in unfolding new era. Now NATO needs a speedy follow-on to the breakthrough decision of the Wales Summit. Cyber defence should be fully integrated into the next Strategic Concept which is expected in or around 2020 but could be worked out sooner because of the accelerating transition of the security environment. NATO should also consider establishing a global Cyber Command to maintain the initiative and to assure the credibility of the enlarged meaning of Article 5 of the North Atlantic Treaty. This credibility will be immediately, continuously and comprehensively tested by many players of the global game.

scholarly journals A Model Analysis of the Behavior of the Mediterranean Water in the North Atlantic

2007 ◽  
Vol 37 (3) ◽  
pp. 764-786 ◽  
Author(s):  
Yanli Jia ◽  
Andrew C. Coward ◽  
Beverly A. de Cuevas ◽  
David J. Webb ◽  
Sybren S. Drijfhout
Keyword(s):  
North Atlantic ◽  
Current System ◽  
Global Ocean ◽  
Western Boundary ◽  
Depth Range ◽  
Strait Of Gibraltar ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
Mediterranean Water

Abstract The behavior of the Mediterranean Water in the North Atlantic Ocean sector of a global ocean general circulation model is explored, starting from its entry point at the Strait of Gibraltar. The analysis focuses primarily on one experiment in which explicit watermass exchange between the Mediterranean Sea and the Atlantic at the Strait of Gibraltar is permitted. The model produces an exchange rate of approximately 1 Sv (Sv ≡ 106 m3 s−1). This is comparable to estimates derived from field measurements. The density of the Mediterranean outflow, however, is lower than observed, mainly because of its high temperature (more than 2°C higher than in reality). The lower density of the outflow and the model’s inadequate representation of the entrainment mixing in the outflow region cause the Mediterranean Water to settle in a depth range ∼800–1000 m in the North Atlantic, about 200 m shallower than observed. Here an interesting current system forms in response to the intrusion of the Mediterranean Water, involving three main pathways. In the first, the Mediterranean Water heads roughly westward across the basin and joins the deep western boundary current. In the second, the water travels northward along the eastern boundary reaching as far as Iceland, where it turns westward to participate in the deep circulation of the subpolar gyre. In the third, the water initially moves westward to the central Atlantic just north of 30°N before turning northwestward to reach an upwelling region at the Grand Banks off Newfoundland. At this location, the saline Mediterranean Water is drawn upward to the ocean upper layer and entrained into the North Atlantic Current system flowing to the northeastern basin; part of the current system enters the Nordic seas.

scholarly journals Assimilation of Radiocarbon and Chlorofluorocarbon Data to Constrain Deep and Bottom Water Transports in the World Ocean

2007 ◽  
Vol 37 (2) ◽  
pp. 259-276 ◽  
Author(s):  
Reiner Schlitzer
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Bottom Water ◽  
World Ocean ◽  
Weddell Sea ◽  
Global Ocean ◽  
Western Boundary ◽  
Boundary Current ◽  
The North ◽  
The North Atlantic

Abstract A coarse-resolution global model with time-invariant circulation is fitted to hydrographic and tracer data by means of the adjoint method. Radiocarbon and chlorofluorocarbon (CFC-11 and CFC-12) data are included to constrain deep and bottom water transport rates and spreading pathways as well as the strength of the global overturning circulation. It is shown that realistic global ocean distributions of hydrographic parameters and tracers can be obtained simultaneously. The model correctly reproduces the deep ocean radiocarbon field and the concentrations gradients between different basins. The spreading of CFC plumes in the deep and bottom waters is simulated in a realistic way, and the spatial extent as well as the temporal evolution of these plumes agrees well with observations. Radiocarbon and CFC observations place upper bounds on the northward transports of Antarctic Bottom Water (AABW) into the Pacific, Atlantic, and Indian Oceans. Long-term mean AABW transports larger than 5 Sv (Sv ≡ 106 m3 s−1) through the Vema and Hunter Channels in the South Atlantic and net AABW transports across 30°S into the Indian Ocean larger than 10 Sv are found to be incompatible with CFC data. The rates of equatorward deep and bottom water transports from the North Atlantic and Southern Ocean are of similar magnitude (15.7 Sv at 50°N and 17.9 Sv at 50°S). Deep and bottom water formation in the Southern Ocean occurs at multiple sites around the Antarctic continent and is not confined to the Weddell Sea. A CFC forecast based on the assumption of unchanged abyssal transports shows that by 2030 the entire deep west Atlantic exhibits CFC-11 concentrations larger than 0.1 pmol kg−1, while most of the deep Indian and Pacific Oceans remain CFC free. By 2020 the predicted CFC concentrations in the deep western boundary current (DWBC) in the North Atlantic exceed surface water concentrations and the vertical CFC gradients start to reverse.

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