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

Abstract

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 (A T ), pH and total inorganic carbon (C T ) 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 ( ) 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 were generally low, coinciding with low Chl a concentrations. The lowest pH in situ and lowest aragonite saturation ( Ar ∼ 1.0) were observed in December 2007 in the coastal Amundsen and Ross seas near marine outflowing glaciers. These low and high pH values were likely influenced by freshwater dilution. Comparing 2007 and 2010, the largest Ar difference was found in the eastern Ross Sea, where Ar 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 CO 2 -rich sub-surface water, likely promoting primary production leading to high and pH. Results from multivariate analysis agree with our observations showing that changes in Chl a had the largest influence on the Ar variability. The future changes of Ar were estimated using reported rates of the oceanic uptake of anthropogenic CO 2 , 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.

Impact of elevated pH on succession in the Arctic spring bloom

“…During the 2011 and 2012 spring blooms in Disko Bay, pH ranged from 7.6 to 8.5. This range in pH is similar to what has been observed in many temperate and tropical coastal waters (Provoost et al 2010, Brutemark et al 2011, Praveena & Aris 2013 and is consistent with the few existing measurements from Arctic and Antarctic waters (Charalampopoulou et al 2011, Yakushev & Sørensen 2013, Mattsdotter Björk et al 2014. Although pH did not exceed 8.5 in Disko Bay, pH may exceed this value in other parts of the Arctic region where high accumulations of phytoplankton biomass occur, e.g.…”

“…The shrinking ice cover has resulted in increased annual primary production in large parts of the Arctic along with significant increases in annual net CO 2 fixation rates (Arrigo et al 2008, Pabi et al 2008, Slagstad et al 2011. Changes in seawater carbon chemistry are known to affect natural plankton communities, but until now most studies in the polar regions have focused on the impact of CO 2 enrichment (ocean acidification) caused by increased atmospheric pCO 2 (Rost et al 2008, Aberle et al 2013, Trimborn et al 2013, Mattsdotter Björk et al 2014. By the end of 2100, surface water pH in the Arctic region is predicted to decrease from an average of ~8.2 at present to ~7.6 (IPCC 2013).…”

Effect of glacial drainage water on the CO2 system and ocean acidification state in an Arctic tidewater‐glacier fjord during two contrasting years

“…The A T values in melted glacial ice were determined using an automated system for potentiometric titration in an open cell using 0.05 N HCl (Methrohm © Titrando system, Switzerland), as described in Mattsdotter‐Björk et al . []. The average standard deviation for A T , determined from replicate sample analyses from one sample, was within ±1 μmol kg −1 for water samples.…”

Contrasting futures for ocean and society from different anthropogenic CO 2 emissions scenarios

“…The largest absolute decrease in aragonite saturation is projected for the tropical ocean, partly modulated by variability within coral reef sites (33,34). Seasonally undersaturated conditions are already present in the northeastern Pacific and the California upwelling system (17) and in the Arctic Ocean (35) and expected for the Southern Ocean (36). pH reductions at the sea floor below 500-m depth, which includes biodiversity hot spots such as deep-sea canyons and seamounts, are SCIENCE sciencemag.org 3 projected to exceed 0.2 units (the likely bound of natural variability over the past hundreds of thousands of years) by 2100 in close to 23% of North Atlantic deep-sea canyons and 8% of seamounts under RCP8.5-including sites proposed as marine protected areas (37).…”