scholarly journals Ocean acidification state in western Antarctic surface waters: drivers and interannual variability

2013 ◽  
Vol 10 (5) ◽  
pp. 7879-7916 ◽  
Author(s):  
M. Mattsdotter Björk ◽  
A. Fransson ◽  
M. Chierici
Keyword(s):  
Surface Water ◽  
Sea Ice ◽  
Interannual Variability ◽  
Chlorophyll A ◽  
Total Alkalinity ◽  
Full Description ◽  
Carbonate System ◽  
Amundsen Sea ◽  
Water Carbonate

Abstract. Each December during four years from 2006 to 2010, the surface water carbonate system was measured and investigated in the Amundsen Sea and Ross Sea, western Antarctica as part of the Oden Southern Ocean expeditions (OSO). The I/B Oden started in Punta Arenas in Chile and sailed southwest, passing through different regimes such as, the marginal/seasonal ice zone, fronts, coastal shelves, and polynyas. Discrete surface water was sampled underway for analysis of total alkalinity (AT), total dissolved inorganic carbon (CT) and pH. Two of these parameters were used together with sea-surface temperature (SST), and salinity to obtain a full description of the surface water carbonate system, including pH in situ and calcium carbonate saturation state of aragonite (ΩAr) and calcite (ΩCa). Multivariate analysis was used to investigate interannual variability and the major controls (sea-ice concentration, SST, salinity and chlorophyll a) on the variability in the carbonate system and Ω. This analysis showed that SST and chlorophyll a were the major drivers of the Ω variability in both the Amundsen and Ross seas. In 2007, the sea-ice edge was located further south and the area of the open polynya was relatively small compared to 2010. We found the lowest pH in situ (7.932) and Ω = 1 values in the sea-ice zone and in the coastal Amundsen Sea, nearby marine out flowing glaciers. In 2010, the sea-ice coverage was the largest and the areas of the open polynyas were the largest for the whole period. This year we found the lowest salinity and AT, coinciding with highest chl a. This implies that the highest ΩAr in 2010 was likely an effect of biological CO2 drawdown, which out-competed the dilution of carbonate ion concentration due to large melt water volumes. We predict and discuss future Ω values, using our data and reported rates of oceanic uptake of anthropogenic CO2, suggesting that the Amundsen Sea will become undersaturated with regard to aragonite about 20 yr sooner than predicted by models.

scholarly journals Ocean acidification state in western Antarctic surface waters: controls and interannual variability

2014 ◽  
Vol 11 (1) ◽  
pp. 57-73 ◽  
Author(s):  
M. Mattsdotter Björk ◽  
A. Fransson ◽  
A. Torstensson ◽  
M. Chierici
Keyword(s):  
Surface Water ◽  
Sea Ice ◽  
Primary Production ◽  
Interannual Variability ◽  
Ross Sea ◽  
Total Alkalinity ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
Saturation State ◽  
Chl A

Abstract. During four austral summers (December to January) from 2006 to 2010, we investigated the surface-water carbonate system and its controls in the western Antarctic Ocean. Measurements of total alkalinity (AT), pH and total inorganic carbon (CT) were investigated in combination with high-frequency measurements on sea-surface temperature (SST), salinity and Chl a. In all parameters we found large interannual variability due to differences in sea-ice concentration, physical processes and primary production. The main result from our observations suggests that primary production was the major control on the calcium carbonate saturation state (Ω) in austral summer for all years. This was mainly reflected in the covariance of pH and Chl a. In the sea-ice-covered parts of the study area, pH and Ω were generally low, coinciding with low Chl a concentrations. The lowest pH in situ and lowest aragonite saturation (ΩAr ~ 1.0) were observed in December 2007 in the coastal Amundsen and Ross seas near marine outflowing glaciers. These low Ω and high pH values were likely influenced by freshwater dilution. Comparing 2007 and 2010, the largest ΩAr difference was found in the eastern Ross Sea, where ΩAr was about 1.2 units lower in 2007 than in 2010. This was mainly explained by differences in Chl a (i.e primary production). In 2010 the surface water along the Ross Sea shelf was the warmest and most saline, indicating upwelling of nutrient and CO2-rich sub-surface water, likely promoting primary production leading to high Ω and pH. Results from multivariate analysis agree with our observations showing that changes in Chl a had the largest influence on the ΩAr variability. The future changes of ΩAr were estimated using reported rates of the oceanic uptake of anthropogenic CO2, combined with our data on total alkalinity, SST and salinity (summer situation). Our study suggests that the Amundsen Sea will become undersaturated with regard to aragonite about 40 yr sooner than predicted by models.

scholarly journals Rapid changes in surface water carbonate chemistry during Antarctic sea ice melt

Tellus B ◽  
2010 ◽  
Vol 62 (5) ◽  
pp. 621-635 ◽  
Author(s):  
Elizabeth Jones ◽  
Dorothee Bakker ◽  
Hugh Venables ◽  
Michael Whitehouse ◽  
Rebecc Korb ◽  
...  
Keyword(s):  
Surface Water ◽  
Sea Ice ◽  
Carbonate Chemistry ◽  
Ice Melt ◽  
Antarctic Sea Ice ◽  
Rapid Changes ◽  
Water Carbonate

scholarly journals Evidence for preindustrial variations in the marine surface water carbonate system from coralline sponges

2002 ◽  
Vol 3 (3) ◽  
pp. 1-13 ◽  
Author(s):  
F. Böhm ◽  
A. Haase-Schramm ◽  
A. Eisenhauer ◽  
W.-C. Dullo ◽  
M. M. Joachimski ◽  
...  
Keyword(s):  
Surface Water ◽  
Carbonate System ◽  
Marine Surface ◽  
Water Carbonate

scholarly journals Current estimates of K<sub>1</sub>* and K<sub>2</sub>* appear inconsistent with measured CO<sub>2</sub> system parameters in cold oceanic regions

Ocean Science ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 847-862 ◽  
Author(s):  
Olivier Sulpis ◽  
Siv K. Lauvset ◽  
Mathilde Hagens
Keyword(s):  
Surface Water ◽  
Ocean Acidification ◽  
Carbonic Acid ◽  
Dissolved Inorganic Carbon ◽  
Dissociation Constants ◽  
Total Alkalinity ◽  
Global Ocean ◽  
Polar Regions ◽  
Carbonate System ◽  
System Variables

Abstract. Seawater absorption of anthropogenic atmospheric carbon dioxide (CO2) has led to a range of changes in carbonate chemistry, collectively referred to as ocean acidification. Stoichiometric dissociation constants used to convert measured carbonate system variables (pH, pCO2, dissolved inorganic carbon, total alkalinity) into globally comparable parameters are crucial for accurately quantifying these changes. The temperature and salinity coefficients of these constants have generally been experimentally derived under controlled laboratory conditions. Here, we use field measurements of carbonate system variables taken from the Global Ocean Data Analysis Project version 2 and the Surface Ocean CO2 Atlas data products to evaluate the temperature dependence of the carbonic acid stoichiometric dissociation constants. By applying a novel iterative procedure to a large dataset of 948 surface-water, quality-controlled samples where four carbonate system variables were independently measured, we show that the set of equations published by Lueker et al. (2000), currently preferred by the ocean acidification community, overestimates the stoichiometric dissociation constants at temperatures below about 8 ∘C. We apply these newly derived temperature coefficients to high-latitude Argo float and cruise data to quantify the effects on surface-water pCO2 and calcite saturation states. These findings highlight the critical implications of uncertainty in stoichiometric dissociation constants for future projections of ocean acidification in polar regions and the need to improve knowledge of what causes the CO2 system inconsistencies in cold waters.

scholarly journals Impact of snow cover on CO<sub>2</sub> dynamics in Antarctic pack ice

2014 ◽  
Vol 8 (3) ◽  
pp. 3263-3295
Author(s):  
N.-X. Geilfus ◽  
J.-L. Tison ◽  
S. F. Ackley ◽  
S. Rysgaard ◽  
L. A. Miller ◽  
...  
Keyword(s):  
Sea Ice ◽  
Snow Cover ◽  
Dissolved Inorganic Carbon ◽  
Ice Cover ◽  
Snow Accumulation ◽  
Total Alkalinity ◽  
Partial Pressures ◽  
Pack Ice ◽  
Cold Events

Abstract. Temporal evolution of pCO2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows that the CO2 system in the ice was primarily controlled by physical and thermodynamic processes. During the survey, a succession of warming and cold events strongly influenced the physical, chemical and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm) and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We confirm that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA), total dissolved inorganic carbon (TCO2), and in situ brine and bulk ice CO2 partial pressures (pCO2). Thicker snow covers muted these changes, suggesting that snow influences changes in the sea ice carbonate system through its impact on the temperature and salinity of the sea ice cover. During this survey, pCO2 was undersaturated with respect to the atmosphere both in situ, in the bulk ice (from 10 to 193 μatm), and in the brine (from 65 to 293 μatm), and the ice acted as a sink for atmospheric CO2 (up to 2.9 mmol m−2 d−1), despite the underlying supersaturated seawater (up to 462 μatm).

scholarly journals Regional-scale phytoplankton dynamics and their association with glacier meltwater runoff in Svalbard

2021 ◽  
Author(s):  
Thorben Dunse ◽  
Kaixing Dong ◽  
Kjetil Schanke Aas ◽  
Leif Christian Stige
Keyword(s):  
Sea Ice ◽  
Chlorophyll A ◽  
Freshwater Discharge ◽  
The Arctic ◽  
Phytoplankton Production ◽  
Phytoplankton Dynamics ◽  
Glacier Meltwater ◽  
Meltwater Runoff ◽  
Glacier Runoff

Abstract. Arctic amplification of global warming has accelerated mass loss of Arctic land ice over the past decades and lead to increased freshwater discharge into glacier fjords and adjacent seas. Glacier freshwater discharge is typically associated with high sediment loads which limits the euphotic depth, but may also provide surface waters with essential nutrients, thus having counter-acting effects on marine productivity. In-situ observations from a few measured fjords across the Arctic indicate that glacier fjords dominated by marine-terminating glaciers are typically more productive than those with only land-terminating glaciers. Here we combine chlorophyll a from satellite ocean colour, an indicator of phytoplankton biomass, with glacier meltwater runoff from climatic mass-balance modelling to establish a statistical model of summertime-phytoplankton dynamics in Svalbard (mid-June to September). Statistical analysis reveals positive spatiotemporal association of chlorophyll a with glacier runoff for 7 out of 14 primary hydrological regions. These regions consist predominantly of the major fjord systems of Svalbard. The adjacent land areas are characterized by a wide range of total glacier coverage (35.5 % to 81.2 %) and fraction of marine-terminating glacier area (40.2 % to 87.4 %). We find that an increase in specific glacier-runoff rate of 10 mm water equivalent per 8-day timeperiod raises summertime chlorophyll a concentrations by 5.2 % to 20.0 %, depending on region. During the annual peak discharge we estimate that glacier runoff contributes to 13.1 % to 50.2 % increase in chlorophyll a compared to situations with no runoff. This suggest that glacier runoff is an important factor sustaining summertime phytoplankton production in Svalbard fjords, in line with findings from several fjords in Greenland. In contrast, for regions bordering open coasts, and beyond 10 km distance from the shore, we do not find significant association of chlorophyll a with runoff. In these regions, physical ocean and sea ice variables control chlorophyll a, pointing at the importance of a late sea ice breakup in northern Svalbard, as well as the advection of Atlantic water masses along the West Spitsbergen Current for summertime phytoplankton dynamics. Our method allows for investigation and monitoring of glacier-runoff effects on primary production throughout the summer season and is applicable on a Pan-Arctic scale, thus complementing valuable but scarce in-situ measurements in both space and time.

New insights into nutrients dynamics and the carbonate system using a neural network approach in the Mediterranean Sea

2020 ◽  
Author(s):  
Marine Fourrier ◽  
Laurent Coppola ◽  
Fabrizio D'Ortenzio
Keyword(s):  
Neural Network ◽  
Mediterranean Sea ◽  
Dissolved Inorganic Carbon ◽  
In Situ Measurements ◽  
Total Alkalinity ◽  
Anthropogenic Pressure ◽  
Carbonate System ◽  
The Mediterranean ◽  
The Impact

&lt;p&gt;The semi-enclosed nature of the Mediterranean Sea, together with its small inertia which is due to the relatively short residence time of its water masses, make it highly reactive to external forcings and anthropogenic pressure. In this context, several rapid changes have been observed in physical and biogeochemical processes in recent decades, partly masked by episodic events and high regional variability. To better understand the underlying processes driving the Mediterranean evolution and, anticipate changes, the measurement, and integration of many biogeochemical variables are mandatory.&lt;/p&gt;&lt;p&gt;The development of new BGC sensors implemented on &lt;em&gt;in situ&lt;/em&gt; autonomous platforms allows to increase the acquisition of essential biogeochemical variables. However, the measurements carried out by&lt;em&gt; in situ&lt;/em&gt; autonomous platforms (e.g. profiling floats, gliders, moorings) are not exhaustive.&lt;/p&gt;&lt;p&gt;Recently, deep learning techniques and in particular neural networks have been developed. The CANYON-MED (for Carbonate system and Nutrients concentration from hYdrological properties and Oxygen using a Neural-network in the MEDiterranean Sea) neural network-based method provides estimations of nutrients (i.e. nitrates, phosphates, and silicates) and carbonate system variables (i.e. total alkalinity, dissolved inorganic carbon, pH&lt;sub&gt;T&lt;/sub&gt;) from systematically measured oceanographic variables such as in situ measurements of pressure, temperature, salinity, and oxygen together with geolocation and date of sampling.&lt;/p&gt;&lt;p&gt;This regional approach, therefore, using quality-controlled in situ measurements from more than 35 cruises. CANYON-MED obtains satisfactory results: accuracies of 0.73, 0.045, and 0.70 &amp;#181;mol.kg&lt;sup&gt;-1&lt;/sup&gt; for the nitrates, phosphates and silicates concentrations respectively, and 0.016, 11 &amp;#181;mol.kg&lt;sup&gt;-1&lt;/sup&gt; and 10 &amp;#181;mol.kg&lt;sup&gt;-1&lt;/sup&gt; for pH&lt;sub&gt;T&lt;/sub&gt;, total alkalinity and dissolved organic carbon respectively. CANYON-MED thus generates &amp;#8220;virtual&amp;#8221; data of parameters not yet measured by autonomous platforms, while ably reproducing the data already sampled, emphasizing its ability to fill the gaps in time-series.&lt;/p&gt;&lt;p&gt;Hence, by applying it to the large and growing network of autonomous platforms in the Mediterranean Sea, this method allows us to gain new insights into nutrients and carbonate system dynamics in targeted areas. In particular, in the northwestern Mediterranean Sea, the impact of deep convection on biogeochemistry (e.g., nutrient replenishment and pH&lt;sub&gt;T&lt;/sub&gt; variability) is highly variable over time and poorly covered by observing networks. In this case, CANYON-MED would improve our observations and understanding of the dynamic and coupled system.&lt;/p&gt;

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