Rapid transition from ice covered CO2-rich waters to a biologically mediated sink in the eastern Weddell Gyre
01 Jan 2007-
TL;DR: Hoppema et al. as discussed by the authors showed that upwelling and ice cover exert an important control on dissolved inorganic carbon (DIC) and the fugacity of carbon dioxide (fCO2) in Weddell Sea surface waters.
Abstract: Upwelling and ice cover exert an important control on dissolved inorganic carbon (DIC) and the fugacity of carbon dioxide (fCO2) in Weddell Sea surface waters in early spring. Ultimately these processes drive CO2 air-sea fluxes. Data were collected during cruise ANT XX/2 on RV Polarstern from December 2002 to January 2003. Deep CTD sections were made along 0°W, a northwest-southeast cross-section and along 20°E. Warm Circumpolar Deep Water (CDW, later WDW) enters the Weddell Gyre on the southeastern side of the gyre, roughly at 20-30°E. The upward movement of this water (upwelling) creates a source for CO2 in the Weddell Gyre. The effects of upwelling and entrainment on surface water characteristics were notably large in the southern Weddell Gyre, both at 0°W and 20°E, confirming observations by Gordon and Huber (1990). Entrainment during the winter months had increased the fCO2 difference across the sea surface, dfCO2(w-a), to 20-40 µatm and had preconditioned a CO2 source upon disappearance of the ice cover. Surface water fCO2 was close to the atmospheric value in areas with less upwelling. Once the ice had gone, biological activity locally reduced dfCO2(w-a) to -50 µatm, thus creating CO2 sinks. Despite the tendency of upwelling to cause CO2 oversaturation, the Weddell Gyre may thus still be a CO2 sink on an annual basis. It is probable that the CO2 source originating from upwelling of old, pre-industrial CDW is declining as atmospheric CO2 levels continue to increase (Hoppema, 2004). The relatively small residence time of surface waters in the gyre (2.5 years on average, considerably less in the southern part of the gyre Gordon and Huber, 1990) and prolonged ice cover (up to 8 months per year) partly explain the low anthropogenic CO2 content of bottom waters originating in the Weddell Gyre (Hoppema et al., 2001).
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22 Jul 2020
TL;DR: In this paper, the authors present evidence that the conventional framework for the subpolar Southern Ocean carbon cycle, which attributes a dominant role to the vertical overturning circulation and shelf-sea processes, fundamentally misrepresents the drivers of regional carbon uptake.
Abstract: Open-ocean biology and the horizontal circulation set the rate of carbon uptake in the subpolar Southern Ocean. Global climate is critically sensitive to physical and biogeochemical dynamics in the subpolar Southern Ocean, since it is here that deep, carbon-rich layers of the world ocean outcrop and exchange carbon with the atmosphere. Here, we present evidence that the conventional framework for the subpolar Southern Ocean carbon cycle, which attributes a dominant role to the vertical overturning circulation and shelf-sea processes, fundamentally misrepresents the drivers of regional carbon uptake. Observations in the Weddell Gyre—a key representative region of the subpolar Southern Ocean—show that the rate of carbon uptake is set by an interplay between the Gyre’s horizontal circulation and the remineralization at mid-depths of organic carbon sourced from biological production in the central gyre. These results demonstrate that reframing the carbon cycle of the subpolar Southern Ocean is an essential step to better define its role in past and future climate change.
15 citations
01 Jan 2013
TL;DR: In this article, the authors present an onderzoek illustreert dat het samenvoegen van ~40 jaar aan oceanografische onder-zoeks data tot een hoogwaardige database goed mogelijk is.
Abstract: Koolstofdioxide, CO2, wordt uitgewisseld tussen – en in – de oceanen, het land en de atmosfeer. Door de verbranding van olie, kolen en gas is de mensheid bezig om extra CO2 (‘antropogene CO2’, CO2ant) toe te voegen aan de natuurlijke koolstofkringloop. Om de aldus veranderende koolstofcyclus goed te kunnen begrijpen, is een beter begrip noodzakelijk van de snelheid van de toename van CO2ant in de oceaan, wat eveneens de doelstelling van dit promotieonderzoek was. Het uitgevoerde onderzoek besloeg (i) het verzamelen van nieuwe CO2-gerelateerde meetgegevens in de diepzee, (ii) het samenstellen van een database van nieuwe en historische meetgegevens en (iii) het gebruik van deze database om de toenamesnelheid te bepalen van CO2ant in de Zuid-Atlantische Oceaan. Deze oceaanregio wordt van groot belang geacht voor de opname van CO2ant uit de atmosfeer en het daaropvolgende transport de diepzee in. Tijdens meerdere vaartochten werden enkele duizenden oceaanmonsters met succes geanalyseerd Het onderzoek illustreert dat het samenvoegen van ~40 jaar aan oceanografische onderzoeksdata tot een hoogwaardige database goed mogelijk is. Eveneens wordt gedemonstreerd dat het mogelijk is om de toename van CO2ant in de diepe oceaan op overtuigende wijze vast te stellen – juist in een oceaan die sterke biologische- en stromings-variabiliteit vertoont, en waarvoor niet veel gegevens beschikbaar zijn. De resulaten versterken de bewijsvoering voor het idee dat de Zuid-Atlantische Oceaan verantwoordelijk is voor de opslag van circa 400 miljoen ton CO2ant per jaar, ofwel ~20% van de totale opname door de oceanen.
8 citations
Dissertation•
01 Jan 2017
TL;DR: In this article, the authors investigated the impact of increasing the gridding resolution of input data and proxy variables, and Support vector regression (SVR) and Random Forest Regression (RFR) as alternate machine learning methods.
Abstract: The Southern Ocean plays an important role in mitigating the effects of anthropogenically driven climate change by being a sink for atmospheric carbon, but this is foreseen to change with increasing greenhouse gas emissions. Studies have already shown that Southern Ocean CO2 is subject to interannual variability. Measuring and understanding this change has been difficult due to sparse observational data that is biased toward summer. Machine learning has been successful in estimating CO2 in may parts of the ocean by extrapolating existing data with satellite measurements of proxy variables of CO2. However, in the Southern Ocean machine learning has proven less successful. Large differences between machine learning estimates stem from the paucity of data and complexity of the mechanisms that drive CO2 in the Southern Ocean. In this study the aim is to reduce the uncertainty of estimates, improve the understanding of the drivers, and optimise sampling of CO2 in the Southern Ocean. Improving the estimates of CO2 was achieved by investigating: the impact of increasing the gridding resolution of input data and proxy variables, and Support vector regression (SVR) and Random Forest Regression (RFR) as alternate machine learning methods. It was found that the improvement gained by increasing gridding resolution was minimal and only RFR was able to improve on existing error estimates. Yet, there was good agreement of the seasonal cycle and interannual trends between RFR, SVR and estimates from the literature. The ensemble mean of these methods was used to investigate the variability and interannual trends of CO2 in the Southern Ocean. The analysis showed that wind was the overall driver of dominant decadal interannual trends, being more important during winter due to the increased efficacy of entrainment processes. Moreover, the Indian sector of the Southern Ocean was prominent in driving this interannual variability. Summer interannual variability of CO2 was driven primarily by Chl-a, which responded to basin scale changes in drivers by the complex interaction with underlying physics and possibly sub-mesoscale processes. Lastly CO2 sampling platforms, namely ships, profiling floats and moorings, were tested in an idealised simulated model environment using a machine learning approach. Ships, simulated from existing cruise tracks, failed to adequately resolve CO2 below the uncertainty threshold that is required to resolve the seasonal cycle of Southern Ocean CO2. Eight high frequency sampling
6 citations
References
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TL;DR: In this paper, a digital bathymetric map of the oceans with a horizontal resolution of 1 to 12 kilometers was derived by combining available depth soundings with high-resolution marine gravity information from the Geosat and ERS-1 spacecraft.
Abstract: A digital bathymetric map of the oceans with a horizontal resolution of 1 to 12 kilometers was derived by combining available depth soundings with high-resolution marine gravity information from the Geosat and ERS-1 spacecraft. Previous global bathymetric maps lacked features such as the 1600-kilometer-long Foundation Seamounts chain in the South Pacific. This map shows relations among the distributions of depth, sea floor area, and sea floor age that do not fit the predictions of deterministic models of subsidence due to lithosphere cooling but may be explained by a stochastic model in which randomly distributed reheating events warm the lithosphere and raise the ocean floor.
4,433 citations
TL;DR: The apparent dissociation constants of carbonic acid in seawater were determined as functions of temperature (2-35°C) and salinity (19-43%) at atmospheric pressure by measurement of K'1 and the product K', K' as discussed by the authors.
Abstract: The apparent dissociation constants of carbonic acid in seawater were determined as functions of temperature (2-35°C) and salinity ( 19-43%) at atmospheric pressure by measurement of K’1 and the product K’, K’,. At 35sa salinity and 25°C the measured values were pE1 = 6.600 and pK’2 = 9.115; at 35% and 2°C the measured values were pK’1 = 6.177 and pKPz = 9.431.
3,085 citations
01 Oct 1987
TL;DR: In this paper, the published experimental data of Hansson and Mehrbach et al. have been critically compared after adjustment to a common pH scale based upon total hydrogen ion concentration, and the results have been pooled to yield reliable equations that can be used to estimate pK1∗and pK2∗ for seawater media a salinities from 0 to 40 and at temperatures from 2 to 35°C.
Abstract: The published experimental data of Hansson and of Mehrbach et al. have been critically compared after adjustment to a common pH scale based upon total hydrogen ion concentration. No significant systematic differences are found within the overall experimental error of the data. The results have been pooled to yield reliable equations that can be used to estimate pK1∗and pK2∗ for seawater media a salinities from 0 to 40 and at temperatures from 2 to 35°C.
2,785 citations
01 May 1995
TL;DR: In this article, large-scale features of the Antarctic Circumpolar Current (ACC) were described using all historical hydrographic data available from the Southern Ocean, and the geopotential anomaly of the sea surface relative to 1000 db reveals the highly-sheared eastward flow of the ACC and the strong steering of the current by the ridge system around Antarctica.
Abstract: Large-scale features of the Antarctic Circumpolar Current (ACC) are described using all historical hydrographic data available from the Southern Ocean. The geopotential anomaly of the sea surface relative to 1000 db reveals the highly-sheared eastward flow of the ACC and the strong steering of the current by the ridge system around Antarctica. The near-surface property distributions differentiate the ACC waters from the warmer and saltier waters of the subtropical regimes. The Subtropical Front (STF), interrupted only by South America, marks the northern most extent of subantarctic waters. Distributions of properties on isopycnal surfaces show an abrupt end to the characteristic signal of the Upper Circumpolar Deep Water (UCDW), as this water mass shoals southward and is entrained into the surface mixed layer. This sharp water mass boundary nearly coincides with the southernmost circumpolar streamline passing through Drake Passage. To its south are the weakly-sheared circulations of the subpolar regime. Inspection of many hydrographic crossings of this transition reveals that the poleward edge of the UCD W signal is a reasonable definition of the southern boundary of the ACC. At Drake Passage, three deep-reaching fronts account for most of the ACC transport. Well-established indicators of the Subantarctic Front and Polar Front are traced unbroken around Antarctica. The third deep-reaching front observed to the south of the Polar Front at Drake Passage also continues with similar characteristics as a circumpolar feature. It is called here the southern ACC front. Stations from multiple synoptic transects of these circumpolar fronts are used to describe the average property structure within each ACC zone. Between the STF and the southern boundary of the ACC, the shear transport of the circumpolar current above 3000 m is at all longitudes about 100 Sv (1 Sv = 106 m3 s−) eastward.
2,513 citations
01 Jan 2007
TL;DR: The Guide to best practices for ocean CO2 measurements can be found in this paper, along with a detailed discussion of the recommended standard operating procedures (SOPs) for ocean carbon dioxide measurements.
Abstract: CHAP 1 - Introduction to the Guide
CHAP 2 - Solution chemistry of carbon dioxide in sea water
CHAP 3 - Quality assurance
CHAP 4 - Recommended standard operating procedures (SOPs)
SOP 1 - Water sampling for the parameters of the oceanic carbon dioxide system
SOP 2 - Determination of total dissolved inorganic carbon in sea water
SOP 3a - Determination of total alkalinity in sea water using a closed-cell titration
SOP 3b - Determination of total alkalinity in sea water using an open-cell titration
SOP 4 - Determination of p(CO2) in air that is in equilibrium with a discrete sample of sea water
SOP 5 - Determination of p(CO2) in air that is in equilibrium with a continuous stream of sea water
SOP 6a - Determination of the pH of sea water using a glass/reference electrode cell
SOP 6b - Determination of the pH of sea water using the indicator dye m-cresol purple
SOP 7 - Determination of dissolved organic carbon and total dissolved nitrogen in sea water
SOP 7 en Espanol - Determinacion de carbono organico disuelto y nitrogeno total disuelto en agua de mar
SOP 11 - Gravimetric calibration of the volume of a gas loop using water
SOP 12 - Gravimetric calibration of volume delivered using water
SOP 13 - Gravimetric calibration of volume contained using water
SOP 14 - Procedure for preparing sodium carbonate solutions for the calibration of coulometric CT measurements
SOP 21 - Applying air buoyancy corrections
SOP 22 - Preparation of control charts
SOP 23 - Statistical techniques used in quality assessment
SOP 24 - Calculation of the fugacity of carbon dioxide in the pure gas or in air
CHAP 5 - Physical and thermodynamic data
Errata - to the hard copy of the Guide to best practices for ocean CO2 measurements
2,183 citations