Inorganic carbon and geochemistry measurements from landfast sea ice in Resolute Passage, Nunavut, Canada, as part of the Arctic-ICE project, May - June 2010

We conducted a six-week investigation of the sea ice inorganic carbon system during the winter-spring transition in the Canadian Arctic Archipelago. Samples for the determination of sea ice geochemistry were collected in conjunction with physical and biological parameters as part of the 2010 Arctic-ICE (Arctic - Ice-Covered Ecosystem in a Rapidly Changing Environment) program, a sea ice-based process study in Resolute Passage, Nunavut. The goal of Arctic-ICE was to determine the physical-biological processes controlling the timing of primary production in Arctic landfast sea ice and to better understand the influence of these processes on the drawdown and release of climatically active gases. The field study was conducted from 1 May to 21 June, 2010.

Reefs shift from net accretion to net erosion along a natural environmental gradient

Coral reefs persist in an accretion-erosion balance and ocean acidification resulting from anthropogenic CO2 emissions threatens to shift this balance in favor of net reef erosion. Corals and calcifying algae, largely responsible for reef accretion, are vulnerable to environmental changes associated with ocean acidification, but the direct effects of lower pH on reef erosion has received less attention, particularly in the context of known drivers of bioerosion and natural variability. This study examines the balance between reef accretion and erosion along a well-characterized natural environmental gradient in Kane'ohe Bay, Hawai'i using experimental blocks of coral skeleton. Comparing before and after micro-computed tomography (µCT) scans to quantify net accretion and erosion, we show that, at the small spatial scale of this study (tens of meters), pH was a better predictor of the accretion-erosion balance than environmental drivers suggested by prior studies, including resource availability, temperature, distance from shore, or depth. In addition, this study highlights the fine-scale variation of pH in coastal systems and the importance of microhabitat variation for reef accretion and erosion processes. We demonstrate significant changes in both the mean and variance of pH on the order of meters, providing a local perspective on global increases in pCO2. Our findings suggest that increases in reef erosion, combined with expected decreases in calcification, will accelerate the shift of coral reefs to an erosion-dominated system in a high-CO2 world. This shift will make reefs increasingly susceptible to storm damage and sea-level rise, threatening the maintenance of the ecosystem services that coral reefs provide.

Seawater carbonate chemistry, primary production, biomass and calcification of plankton and bacteria, 2009

Production (abundance and biomass) and net calcification rates of the coccolithophorid Pleurochrysis carterae under different partial pressures of CO2 (pCO2) were examined using short (15, 24 and 39 h), long (7 d) and dark (7 d) incubation experiments. Short incubations were conducted at ambient, 500 and 820 ppm pCO2 levels in natural seawater that was enriched with nutrients and inoculated with P. carterae. Long incubations were conducted at ambient and 1200 ppm pCO2 levels in natural seawater (0.2 µm filtered as well as unfiltered) that was enriched with nutrients and inoculated with P. carterae. Dark incubations were conducted at ambient and 1200 ppm pCO2 in unfiltered seawater that was inoculated with P. carterae. The abundance and biomass of coccolithophorids increased with pCO2 and time. The abundance and biomass of most noncalcifying phytoplankton also increased, and were hardly affected by CO2 inputs. Net calcification rates were negative in short incubations during the pre-bloom phase regardless of pCO2 levels, indicating dissolution of calcium carbonate. Further, the negative values of net calcification in short incubations became less negative with time. Net calcification rates were positive in long incubations during blooms regardless of pCO2 level, and the rate of calcification increased with pCO2. Our results show that P. carterae may adapt to increased (~1200 ppm) pCO2 level with time, and such increase has little effect on the ecology of noncalcifying groups and hence in ecosystem dynamics. In dark incubations, net calcification rates were negative, with the magnitude being dependent on pCO2 levels.

Seawater carbonate chemistry and calcification rate in flume experiment

Ocean acidification (OA) poses a severe threat to tropical coral reefs, yet much of what is know about these effects comes from individual corals and algae incubated in isolation under high pCO2. Studies of similar effects on coral reef communities are scarce. To investigate the response of coral reef communities to OA, we used large outdoor flumes in which communities composed of calcified algae, corals, and sediment were combined to match the percentage cover of benthic communities in the shallow back reef of Moorea, French Polynesia. Reef communities in the flumes were exposed to ambient (400 ?atm) and high pCO2 (1300 ?atm) for 8 weeks, and calcification rates measured for the constructed communities including the sediments. Community calcification was reduced by 59% under high pCO2, with sediment dissolution explaining ~ 50% of this decrease; net calcification of corals and calcified algae remained positive but was reduced by 29% under elevated pCO2. These results show that, despite the capacity of coral reef calcifiers to maintain positive net accretion of calcium carbonate under OA conditions, reef communities might transition to net dissolution as pCO2 increases, particularly at night, due to enhanced sediment dissolution.

Limacina helicina size weight relationship in Kongsfjorden Svalbard, May 2009

Thecosome pteropods (pelagic mollusks) can play a key role in the food web of various marine ecosystems. They are a food source for zooplankton or higher predators such as fishes, whales and birds that is particularly important in high latitude areas. Since they harbor a highly soluble aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The effect of changes in the seawater chemistry was investigated on Limacina helicina, a key species of Arctic pelagic ecosystems. Individuals were kept in the laboratory under controlled pCO2 levels of 280, 380, 550, 760 and 1020 µatm and at control (0°C) and elevated (4°C) temperatures. The respiration rate was unaffected by pCO2 at control temperature, but significantly increased as a function of the pCO2 level at elevated temperature. pCO2 had no effect on the gut clearance rate at either temperature. Precipitation of CaCO3, measured as the incorporation of 45Ca, significantly declined as a function of pCO2 at both temperatures. The decrease in calcium carbonate precipitation was highly correlated to the aragonite saturation state. Even though this study demonstrates that pteropods are able to precipitate calcium carbonate at low aragonite saturation state, the results support the current concern for the future of Arctic pteropods, as the production of their shell appears to be very sensitive to decreased pH. A decline of pteropod populations would likely cause dramatic changes to various pelagic ecosystems.