scholarly journals Interannual-to-decadal variability of North Atlantic air-sea CO<sub>2</sub> fluxes

2005 ◽  
Vol 2 (4) ◽  
pp. 437-472 ◽  
Author(s):  
S. Raynaud ◽  
O. Aumont ◽  
K. B. Rodgers ◽  
P. Yiou ◽  
J. C. Orr
Keyword(s):  
North Atlantic ◽  
Co2 Flux ◽  
Atmospheric Co2 ◽  
Global Ocean ◽  
Co2 Fluxes ◽  
The North ◽  
Basin Scale ◽  
The North Atlantic ◽  
Ocean Models ◽  
Atmospheric Inversions

Abstract. The magnitude of the interannual variability of North Atlantic air-sea CO2 fluxes remains uncertain. Fluxes inferred from atmospheric inversions have large variability, whereas those simulated by ocean models have small variability. Part of the difference is that unlike typical atmospheric inversions, ocean models come with spatial resolution at the sub-basin scale. Here we explore sub-basin-scale spatiotemporal variability in the North Atlantic in one ocean model in order to better understand why the the North Atlantic basin may well contribute very little to the global variability of air-sea CO2 flux. We made two simulations with a biogeochemical model coupled to a global ocean general circulation model (OGCM), which itself was forced by 55-year NCEP reanalysis fields. In the first simulation, atmospheric CO2 was maintained at the preindustrial level (278 ppmv); in the second simulation, atmospheric CO2 followed the observed increase. Simulated air-sea CO2 fluxes and associated variables were analysed with a statistical tool known as multichannel singular spectrum analysis (MSSA). We found that the subtropical gyre is not the largest contributor to the overall, basin-wide variability, in contrast to previous suggestions. The subpolar gyre and the inter-gyre region (the transition area between subpolar and subtropical gyres) also contribute with multipolar anomalies at multiple frequencies: these tend to cancel one another in terms of the basin-wide air-sea CO2 flux. We found a strong correlation between the air-sea CO2 fluxes and the North Atlantic Oscillation (NAO), but only if one takes into account time lags as does MSSA (maximum r=0.64 for lags between 1 and 3 years). The contribution of anthropogenic CO2 to total variability was negligible at interannual time scales, whereas at the decadal (13-year) time scale, it increased variability by 30%.

scholarly journals Interannual-to-decadal variability of North Atlantic air-sea CO<sub>2</sub> fluxes

Ocean Science ◽  
2006 ◽  
Vol 2 (1) ◽  
pp. 43-60 ◽  
Author(s):  
S. Raynaud ◽  
J. C. Orr ◽  
O. Aumont ◽  
K. B. Rodgers ◽  
P. Yiou
Keyword(s):  
North Atlantic ◽  
Atmospheric Co2 ◽  
Spatiotemporal Variability ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Time Lags ◽  
Co2 Fluxes ◽  
The North ◽  
Wide Variability ◽  
The North Atlantic

Abstract. The magnitude of the interannual variability of North Atlantic air-sea CO2 fluxes remains uncertain. Interannual extremes simulated by atmospheric inverse approaches are typically about ±0.3 Pg C yr−1, whereas those from ocean models are less than ±0.1 Pg C yr−1. Thus variability in the North Atlantic is either about 60% or less than 20% of the global variability of about ±0.5 Pg C yr−1 (as estimated by both approaches). Here we explore spatiotemporal variability within the North Atlantic basin of one ocean model in order to more fully describe potential counteracting trends in different regions that may explain why basin-wide variability is small relative to global-scale variability. Typical atmospheric inverse approaches separate the North Atlantic into at most a few regions and thus cannot properly simulate such counteracting effects. For this study, two simulations were made with a biogeochemical model coupled to a global ocean general circulation model (OGCM), which itself was forced by 55-year NCEP reanalysis fields. In the first simulation, atmospheric CO2 was maintained at the preindustrial level (278 ppmv); in the second simulation, atmospheric CO2 followed the observed increase. Simulated air-sea CO2 fluxes and associated variables were then analysed with a statistical tool known as multichannel singular spectrum analysis (MSSA). We found that the subtropical gyre is not the largest contributor to the overall, basin-wide variability, in contrast to previous suggestions. The subpolar gyre and the inter-gyre region (the transition area between subpolar and subtropical gyres) also contribute with multipolar anomalies at multiple frequencies: these tend to cancel one another in terms of the basin-wide air-sea CO2 flux. We found a strong correlation between the air-sea CO2 fluxes and the North Atlantic Oscillation (NAO), but only if one takes into account time lags as does MSSA (maximum r=0.64 for lags between 1 and 3 years). The effect of increasing atmospheric CO2 (the anthropogenic perturbation) on total variability was negligible at interannual time scales, whereas at the decadal (13-year) time scale, it increased variability by 30%.

scholarly journals Coccolithophore surface distributions in the North Atlantic and their modulation of the air-sea flux of CO<sub>2</sub> from 10 years of satellite Earth observation data

2013 ◽  
Vol 10 (4) ◽  
pp. 2699-2709 ◽  
Author(s):  
J. D. Shutler ◽  
P. E. Land ◽  
C. W. Brown ◽  
H. S. Findlay ◽  
C. J. Donlon ◽  
...  
Keyword(s):  
North Atlantic ◽  
Southern Oscillation ◽  
Co2 Flux ◽  
Earth Observation ◽  
Atmospheric Co2 ◽  
Wide Field ◽  
Observation Data ◽  
The North ◽  
The North Atlantic ◽  
Earth Observation Data

Abstract. Coccolithophores are the primary oceanic phytoplankton responsible for the production of calcium carbonate (CaCO3). These climatically important plankton play a key role in the oceanic carbon cycle as a major contributor of carbon to the open ocean carbonate pump (~50%) and their calcification can affect the atmosphere-to-ocean (air-sea) uptake of carbon dioxide (CO2) through increasing the seawater partial pressure of CO2 (pCO2). Here we document variations in the areal extent of surface blooms of the globally important coccolithophore, Emiliania huxleyi, in the North Atlantic over a 10-year period (1998–2007), using Earth observation data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). We calculate the annual mean sea surface areal coverage of E. huxleyi in the North Atlantic to be 474 000 ± 104 000 km2, which results in a net CaCO3 carbon (CaCO3-C) production of 0.14–1.71 Tg CaCO3-C per year. However, this surface coverage (and, thus, net production) can fluctuate inter-annually by −54/+8% about the mean value and is strongly correlated with the El Niño/Southern Oscillation (ENSO) climate oscillation index (r=0.75, p<0.02). Our analysis evaluates the spatial extent over which the E. huxleyi blooms in the North Atlantic can increase the pCO2 and, thus, decrease the localised air-sea flux of atmospheric CO2. In regions where the blooms are prevalent, the average reduction in the monthly air-sea CO2 flux can reach 55%. The maximum reduction of the monthly air-sea CO2 flux in the time series is 155%. This work suggests that the high variability, frequency and distribution of these calcifying plankton and their impact on pCO2 should be considered if we are to fully understand the variability of the North Atlantic air-to-sea flux of CO2. We estimate that these blooms can reduce the annual N. Atlantic net sink atmospheric CO2 by between 3–28%.

The Marine Environment

2017 ◽  
Author(s):  
N. Penny Holliday ◽  
Stephanie Henson
Keyword(s):  
Primary Production ◽  
North Atlantic ◽  
Physical Environment ◽  
Seasonal Cycle ◽  
Physical Processes ◽  
The North ◽  
Basin Scale ◽  
The North Atlantic ◽  
Physical Features ◽  
Growth Distribution

The growth, distribution, and variability of phytoplankton populations in the North Atlantic are primarily controlled by the physical environment. This chapter provides an overview of the regional circulation of the North Atlantic, and an introduction to the key physical features and processes that affect ecosystems, and especially plankton, via the availability of light and nutrients. There is a natural seasonal cycle in primary production driven by physical processes that determine the light and nutrient levels, but the pattern has strong regional variations. The variations are determined by persistent features on the basin scale (e.g. the main currents and mixed layer regimes of the subtropical and subpolar gyres), as well as transient mesoscale features such as eddies and meanders of fronts.

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

&lt;p&gt;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&lt;sub&gt;2&lt;/sub&gt; 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.&lt;/p&gt;&lt;p&gt;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&amp;#180;s projected future carbon-uptake. The first indicator is the high latitude summer pCO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;sea&lt;/sup&gt;-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&amp;#180;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.&lt;/p&gt;

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.

Decadal Evolution of Ocean Thermal Anomalies in the North Atlantic: The Effects of Ekman, Overturning, and Horizontal Transport

2014 ◽  
Vol 27 (2) ◽  
pp. 698-719 ◽  
Author(s):  
Richard G. Williams ◽  
Vassil Roussenov ◽  
Doug Smith ◽  
M. Susan Lozier
Keyword(s):  
North Atlantic ◽  
Volume Transport ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Dynamical Analysis ◽  
Thermal Anomalies ◽  
The North ◽  
Basin Scale ◽  
The North Atlantic ◽  
Induced Changes

Abstract Basin-scale thermal anomalies in the North Atlantic, extending to depths of 1–2 km, are more pronounced than the background warming over the last 60 years. A dynamical analysis based on reanalyses of historical data from 1965 to 2000 suggests that these thermal anomalies are formed by ocean heat convergences, augmented by the poorly known air–sea fluxes. The heat convergence is separated into contributions from the horizontal circulation and the meridional overturning circulation (MOC), the latter further separated into Ekman and MOC transport minus Ekman transport (MOC-Ekman) cells. The subtropical thermal anomalies are mainly controlled by wind-induced changes in the Ekman heat convergence, while the subpolar thermal anomalies are controlled by the MOC-Ekman heat convergence; the horizontal heat convergence is generally weaker, only becoming significant within the subpolar gyre. These thermal anomalies often have an opposing sign between the subtropical and subpolar gyres, associated with opposing changes in the meridional volume transport driving the Ekman and MOC-Ekman heat convergences. These changes in gyre-scale convergences in heat transport are probably induced by the winds, as they correlate with the zonal wind stress at gyre boundaries.

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