Interannual variability of pteropod shell weights in the high-CO 2 Southern Ocean

• Main Authors: Roberts, D, Howard, W, Moy, AD, Roberts, JL, Trull, T, Bray, SG, Hopcroft, RR
• Format: Text
• Language: English
• Published: Copernicus Publications 2008
• Subjects: Earth Sciences; Atmospheric Sciences; Climate Change Processes; Southern Ocean; Antarc*; Antarctica; Limacina helicina; Ocean acidification
• Online Access: http://www.biogeosciences.net/; http://ecite.utas.edu.au/56332

Anthropogenic inputs of CO2 are altering ocean chemistry and may alter the role ofmarine calcifiers in ocean ecosystems. CO2 emissions over the coming centuries mayproduce changes in ocean pH not seen for millions of years. Laboratory evidence5 has shown decreased calcification in some species of coccolithophores, foraminifera,corals and pteropods in response to CO2 enrichment. However, in situ observationsof calcification in marine organisms are limited, especially for the aragonitic pteropods.This group of pelagic molluscs are likely to be more sensitive to changes in carbonatechemistry than calcite producers such as foraminifera and coccolithophores. Here10 we present observations of pteropod shell-weight and flux from 19972006 in sedimenttraps deployed at 47 S, 142 E at 2000 meters below sea surface in the SouthernOcean. A decadal trend of 1.170.47 g yr−1 (P =0.02) in mean shell weight in thepteropod Limacina helicina antarctica forma antarctica suggests a small but detectablereduction in calcification. Gaps in the data make it difficult to state with certainty the15 significance of the trend. However, this data set represents the first attempt to estimateinterannual variations in pteropod calcification and establish a benchmark againstwhich future impacts of ocean acidification may be detected. Contributions of Limacinahelicina antarctica morphotypes to the total pteropod flux were also reduced over thedecade. We suggest these small though discernible trends are due to changing car20bonate chemistry in the Subantarctic, as other oceanographic variables show no cleardecadal trends. With CO2 continuing to enter the ocean such impacts on pteropodsand other marine calcifiers could result in changes to the distribution of species andthe structure of Southern Ocean ecosystems.