scholarly journals Storms drive outgassing of CO2 in the subpolar Southern Ocean

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Sarah-Anne Nicholson ◽  
Daniel B. Whitt ◽  
Ilker Fer ◽  
Marcel D. du Plessis ◽  
Alice D. Lebéhot ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Critical Region ◽  
Process Model ◽  
Ekman Transport ◽  
Ocean Turbulence ◽  
Ocean Fronts ◽  
Ocean Variability ◽  
Synoptic Variability ◽  
Ocean Physics ◽  
Global Mean

AbstractThe subpolar Southern Ocean is a critical region where CO2 outgassing influences the global mean air-sea CO2 flux (FCO2). However, the processes controlling the outgassing remain elusive. We show, using a multi-glider dataset combining FCO2 and ocean turbulence, that the air-sea gradient of CO2 (∆pCO2) is modulated by synoptic storm-driven ocean variability (20 µatm, 1–10 days) through two processes. Ekman transport explains 60% of the variability, and entrainment drives strong episodic CO2 outgassing events of 2–4 mol m−2 yr−1. Extrapolation across the subpolar Southern Ocean using a process model shows how ocean fronts spatially modulate synoptic variability in ∆pCO2 (6 µatm2 average) and how spatial variations in stratification influence synoptic entrainment of deeper carbon into the mixed layer (3.5 mol m−2 yr−1 average). These results not only constrain aliased-driven uncertainties in FCO2 but also the effects of synoptic variability on slower seasonal or longer ocean physics-carbon dynamics.

scholarly journals The Seasonal Cycle of Blocking and Associated Physical Mechanisms in the Australian Region and Relationship with Rainfall

2013 ◽  
Vol 141 (12) ◽  
pp. 4534-4553 ◽  
Author(s):  
M. J. Pook ◽  
J. S. Risbey ◽  
P. C. McIntosh ◽  
C. C. Ummenhofer ◽  
A. G. Marshall ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Seasonal Cycle ◽  
Seasonal Temperature ◽  
Ocean Fronts ◽  
Temperature Changes ◽  
Physical Mechanisms ◽  
Australian Region ◽  
Continental Antarctica ◽  
Positive Correlations ◽  
Blocking Index

Abstract The seasonal cycle of blocking in the Australian region is shown to be associated with major seasonal temperature changes over continental Antarctica (approximately 15°–35°C) and Australia (about 8°–17°C) and with minor changes over the surrounding oceans (below 5°C). These changes are superimposed on a favorable background state for blocking in the region resulting from a conjunction of physical influences. These include the geographical configuration and topography of the Australian and Antarctic continents and the positive west to east gradient of sea surface temperature in the Indo-Australian sector of the Southern Ocean. Blocking is represented by a blocking index (BI) developed by the Australian Bureau of Meteorology. The BI has a marked seasonal cycle that reflects seasonal changes in the strength of the westerly winds in the midtroposphere at selected latitudes. Significant correlations between the BI at Australian longitudes and rainfall have been demonstrated in southern and central Australia for the austral autumn, winter, and spring. Patchy positive correlations are evident in the south during summer but significant negative correlations are apparent in the central tropical north. By decomposing the rainfall into its contributions from identifiable synoptic types during the April–October growing season, it is shown that the high correlation between blocking and rainfall in southern Australia is explained by the component of rainfall associated with cutoff lows. These systems form the cyclonic components of blocking dipoles. In contrast, there is no significant correlation between the BI and rainfall from Southern Ocean fronts.

scholarly journals Changes in Local and Global Climate Feedbacks in the Absence of Interactive Clouds: Southern Ocean–Climate Interactions in Two Intermediate-Complexity Models

2021 ◽  
Vol 34 (2) ◽  
pp. 755-772
Author(s):  
Patrik L. Pfister ◽  
Thomas F. Stocker
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Climate Models ◽  
Lapse Rate ◽  
Climate Feedback ◽  
Ocean Heat Uptake ◽  
Albedo Feedback ◽  
Intermediate Complexity ◽  
Global Mean ◽  
Over Time

AbstractThe global-mean climate feedback quantifies how much the climate system will warm in response to a forcing such as increased CO2 concentration. Under a constant forcing, this feedback becomes less negative (increasing) over time in comprehensive climate models, which has been attributed to increases in cloud and lapse-rate feedbacks. However, out of eight Earth system models of intermediate complexity (EMICs) not featuring interactive clouds, two also simulate such a feedback increase: Bern3D-LPX and LOVECLIM. Using these two models, we investigate the causes of the global-mean feedback increase in the absence of cloud feedbacks. In both models, the increase is predominantly driven by processes in the Southern Ocean region. In LOVECLIM, the global-mean increase is mainly due to a local longwave feedback increase in that region, which can be attributed to lapse-rate changes. It is enhanced by the slow atmospheric warming above the Southern Ocean, which is delayed due to regional ocean heat uptake. In Bern3D-LPX, this delayed regional warming is the main driver of the global-mean feedback increase. It acts on a near-constant local feedback pattern mainly determined by the sea ice–albedo feedback. The global-mean feedback increase is limited by the availability of sea ice: faster Southern Ocean sea ice melting due to either stronger forcing or higher equilibrium climate sensitivity (ECS) reduces the increase of the global mean feedback in Bern3D-LPX. In the highest-ECS simulation with 4 × CO2 forcing, the feedback even becomes more negative (decreasing) over time. This reduced ice–albedo feedback due to sea ice depletion is a plausible mechanism for a decreasing feedback also in high-forcing simulations of other models.

scholarly journals Defining Southern Ocean fronts and their influence on biological and physical processes in a changing climate

2020 ◽  
Vol 10 (3) ◽  
pp. 209-219 ◽  
Author(s):  
Christopher C. Chapman ◽  
Mary-Anne Lea ◽  
Amelie Meyer ◽  
Jean-Baptiste Sallée ◽  
Mark Hindell
Keyword(s):  
Southern Ocean ◽  
Physical Processes ◽  
Ocean Fronts ◽  
Changing Climate

scholarly journals Deep Bottom Mixed Layer Drives Intrinsic Variability of the Antarctic Slope Front

2019 ◽  
Vol 49 (12) ◽  
pp. 3163-3177 ◽  
Author(s):  
Wilma Gertrud Charlotte Huneke ◽  
Andreas Klocker ◽  
Benjamin Keith Galton-Fenzi
Keyword(s):  
Continental Shelf ◽  
Mixed Layer ◽  
Process Model ◽  
Formation Rate ◽  
Ekman Transport ◽  
Intrinsic Variability ◽  
Subsequent Increase ◽  
The Stability ◽  
Basal Melting ◽  
The Antarctic

AbstractThe Antarctic Slope Front (ASF) is located along much of the Antarctic continental shelf break and helps to maintain a barrier to the movement of Circumpolar Deep Water (CDW) onto the continental shelf. The stability of the ASF has a major control on cross-shelf heat transport and ocean-driven basal melting of Antarctic ice shelves. Here, the ASF dynamics are investigated for continental shelves with weak dense shelf water (DSW) formation, which are thought to have a stable ASF, common for regions in East Antarctica. Using an ocean process model, this study demonstrates how offshore bottom Ekman transport of shelf waters leads to the development of a deep bottom mixed layer at the lower continental slope, and subsequently determines an intrinsic variability of the ASF. The ASF variability is characterized by instability events that affect the entire water column and occur every 5–10 years and last for approximately half a year. During these instability events, the cross-shelf density gradient weakens and CDW moves closer to the continent. Stronger winds increase the formation rate of the bottom mixed layer, which causes a subsequent increase of instability events. If the observed freshening trend of continental shelf waters leads to weaker DSW formation, more regions might be vulnerable for the ASF variability to develop in the future.

The Role of Mesoscale Eddies in the Rectification of the Southern Ocean Response to Climate Change

2010 ◽  
Vol 40 (7) ◽  
pp. 1539-1557 ◽  
Author(s):  
Riccardo Farneti ◽  
Thomas L. Delworth ◽  
Anthony J. Rosati ◽  
Stephen M. Griffies ◽  
Fanrong Zeng
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
Climate Model ◽  
Coupled Model ◽  
Ekman Transport ◽  
Dynamical Response ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Climate Change Scenarios ◽  
Residual Circulation ◽  
Atmospheric Changes

Abstract Simulations from a fine-resolution global coupled model, the Geophysical Fluid Dynamics Laboratory Climate Model, version 2.4 (CM2.4), are presented, and the results are compared with a coarse version of the same coupled model, CM2.1, under idealized climate change scenarios. A particular focus is given to the dynamical response of the Southern Ocean and the role played by the eddies—parameterized or permitted—in setting the residual circulation and meridional density structure. Compared to the case in which eddies are parameterized and consistent with recent observational and idealized modeling studies, the eddy-permitting integrations of CM2.4 show that eddy activity is greatly energized with increasing mechanical and buoyancy forcings, buffering the ocean to atmospheric changes, and the magnitude of the residual oceanic circulation response is thus greatly reduced. Although compensation is far from being perfect, changes in poleward eddy fluxes partially compensate for the enhanced equatorward Ekman transport, leading to weak modifications in local isopycnal slopes, transport by the Antarctic Circumpolar Current, and overturning circulation. Since the presence of active ocean eddy dynamics buffers the oceanic response to atmospheric changes, the associated atmospheric response to those reduced ocean changes is also weakened. Further, it is hypothesized that present numerical approaches for the parameterization of eddy-induced transports could be too restrictive and prevent coarse-resolution models from faithfully representing the eddy response to variability and change in the forcing fields.

Variability of the Southern Ocean fronts at the Greenwich Meridian

2010 ◽  
Vol 82 (4) ◽  
pp. 304-310 ◽  
Author(s):  
W. Billany ◽  
S. Swart ◽  
J. Hermes ◽  
C.J.C. Reason
Keyword(s):  
Southern Ocean ◽  
Ocean Fronts ◽  
Greenwich Meridian

Structure of Southern Ocean fronts at 140°E

2002 ◽  
Vol 37 (1-3) ◽  
pp. 151-184 ◽  
Author(s):  
Serguei Sokolov ◽  
Stephen R Rintoul
Keyword(s):  
Southern Ocean ◽  
Ocean Fronts

scholarly journals An empirical stochastic model of sea-surface temperature and surface wind over the Southern Ocean

2011 ◽  
Vol 8 (4) ◽  
pp. 1891-1936
Author(s):  
S. Kravtsov ◽  
D. Kondrashov ◽  
I. Kamenkovich ◽  
M. Ghil
Keyword(s):  
Southern Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Singular Spectrum Analysis ◽  
Surface Wind ◽  
Preliminary Evidence ◽  
Sea Surface ◽  
Satellite Measurements ◽  
Synoptic Variability ◽  
Ocean Region

Abstract. This study employs NASA's recent satellite measurements of sea-surface temperature (SST) and sea-level wind (SLW) with missing data filled-in by Singular Spectrum Analysis (SSA), to construct empirical models that capture both intrinsic and SST-dependent aspects of SLW variability. The model construction methodology uses a number of algorithmic innovations that are essential in providing stable estimates of model's propagator. The best model tested herein is able to faithfully represent the time scales and spatial patterns of anomalies associated with a number of distinct processes. These processes range from the daily synoptic variability to interannual signals presumably associated with oceanic or coupled dynamics. Comparing the simulations of an SLW model forced by the observed SST anomalies with the simulations of an SLW-only model provides preliminary evidence for the climatic behavior characterized by the ocean driving the atmosphere in the Southern Ocean region.

Suppression of air-sea CO2 transfer by surfactants – direct evidence from the Southern Ocean

2021 ◽  
Author(s):  
Mingxi Yang ◽  
Timothy Smyth ◽  
Vassilis Kitidis ◽  
Ian Brown ◽  
Charel Wohl ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Direct Evidence ◽  
Gas Transfer ◽  
Climate Projections ◽  
Transfer Velocity ◽  
Wind Speeds ◽  
Naturally Occurring ◽  
Mean Wind Speed ◽  
Surface Active ◽  
Global Mean

<p>Uncertainty in the CO<sub>2</sub> gas transfer velocity (K<sub>660</sub>) severely limits the accuracy of air-sea CO<sub>2</sub> flux calculations and hence hinders our ability to produce realistic climate projections.  Recent field observations have suggested substantial variability in K<sub>660</sub>, especially at low and high wind speeds.  Laboratory experiments have shown that naturally occurring surface active organic materials, or surfactants, can suppress gas transfer.  Here we provide direct open ocean evidence of gas transfer suppression due to surfactants from a ~11,000 km long research expedition by making measurements of the gas transfer efficiency (GTE) along with direct observation of K<sub>660</sub>.  GTE varied by 20% during the Southern Ocean transect and was distinct in different watermasses.  Furthermore GTE correlated with and can explain about 9% of the scatter in K<sub>660</sub>, suggesting that surfactants exert a measurable influence on air-sea CO<sub>2</sub> flux.  Relative gas transfer suppression due to surfactants was ~30% at a global mean wind speed of 7 m s<sup>-1</sup> and was more important at lower wind speeds.  Neglecting surfactant suppression may result in substantial spatial and temporal biases in the computed air-sea CO<sub>2</sub> fluxes.</p>

Diapycnal and Isopycnal Transports in the Southern Ocean Estimated by a Box Inverse Model

2013 ◽  
Vol 43 (11) ◽  
pp. 2270-2287 ◽  
Author(s):  
K. Katsumata ◽  
B. M. Sloyan ◽  
S. Masuda
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Deep Water ◽  
General Circulation ◽  
General Circulation Models ◽  
Inverse Model ◽  
Ekman Transport ◽  
Surface Mixed Layer ◽  
Circumpolar Deep Water ◽  
Eddy Transport

Abstract Quantitative descriptions of Circumpolar Deep Water upwelling and evolution into a lighter mode and heavier bottom waters in the Southern Ocean are still not well constrained. Here, data from two occupations of eight hydrographic sections are combined and used in a box inverse model to estimate isopycnal and diapycnal transports in the Southern Ocean. A mixed layer box allows diapycnal transports in the surface mixed layer to be estimated separately. Current velocity at 1000 dbar was constrained by the mean velocity field estimated from subsurface float drift data. The estimated isopycnal transports are largely consistent with past estimates and with outputs of three ocean general circulation models. The estimated subduction and upwelling at the base of the Southern Ocean mixed layer show that Upper Circumpolar Deep Water upwells [16 ± 15 and 17 ± 21 Sv (where 1 Sv ≡ 106 m3 s−1) by different inversion methods] and evolves into heavier Lower Circumpolar Deep Water (5 ± 13 and 6 ± 18 Sv) and Bottom Water (8 ± 9 and 8 ± 13 Sv) or lighter Mode and Intermediate Waters (9 ± 18 and 13 ± 24 Sv). Meridional transport in the surface mixed layer is due to northward Ekman transport and mostly southward eddy transport. In seasonal ice-covered areas near Antarctica, a significant (14 ± 14 Sv) southward transport was found. The southward eddy transport is largest north of the Antarctic Circumpolar Current and decreases poleward because of the poleward decrease in the eddy diffusivity. The interior diapycnal transports, which can be either upward (gaining buoyancy) or downward (gaining density), are comparable in magnitude to the horizontal diapycnal transports within the surface mixed layer.

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