Potential impact of increased temperature and CO₂ on particulate dimethylsulfoniopropionate in the Southeastern Bering Sea

Abstract

The potential impact of elevated sea surface temperature (SST) and pCO₂ on algal community structure and particulate dimethylsulfoniopropionate (DMSP_p) concentrations in the southeastern Bering Sea was examined using a shipboard “Ecostat” continuous culture system. The ecostat system was used to mimic the conditions projected to exist in the world's oceans by the end of this century (i.e. elevated pCO₂ (750 ppm) and elevated SST (ambient + 4°C). Two experiments were conducted using natural phytoplankton assemblages from the high-nutrient low-chlorophyll (HNLC) central basin and from the middle domain of the southeastern continental shelf. At the HNLC site, the relative abundances of haptophytes and pelagophytes were higher and the relative abundance of diatoms lower under “greenhouse” conditions (i.e. combined 750 ppm CO₂ and elevated temperature) than control conditions (380 ppm CO₂ and ambient temperature). This shift in algal community structure was accompanied by increases in DMSP_p (2–3 fold), DMSP_p:Chl a (2–3 fold) and DMSP:PON (2 fold). At the continental shelf site, the changes in the relative abundances of haptophytes, pelagophytes and diatoms under “greenhouse” conditions were similar to those observed at the HNLC site, with 2.5 fold increases in DMSP_p, 50–100% increases in DMSP_p:Chl a and 1.8 fold increases in DMSP:PON. At both locations, changes in community structure and the DMSP_p parameters were largely driven by increasing temperature. The observed changes were also consistent with the phytoplankton-DMS-albedo climate feedback mechanism proposed in the Charlson-Lovelock-Andreae-Warren (CLAW) hypothesis.

Keywords:

• climate feedback
• global warming
• temperature
• carbon dioxide
• phytoplankton community structure
• DMSP

Acknowledgements

The authors would like to thank the captain and crew of the R/V Kilo Moana and chief scientist Ken Bruland for their support. The authors also gratefully acknowledge J.M. Rose (Biology Dept., WHOI) for assistance with the statistical analyses and two anonymous reviewers whose constructive criticisms greatly improved the manuscript. This study has been made possible through funding from the Biological and Chemical Oceanography Programs of the US National Science Foundation (OCE-0104190 and OCE-0327620 to GRD; OCE 0722337 and OCE-0825319 to DAH).