Changes in biogenic carbon flow in response to sea surface warming

Abstract

The pelagic ocean harbors one of the largest ecosystems on Earth. It is responsible for approximately half of global primary production, sustains worldwide fisheries, and plays an important role in the global carbon cycle. Ocean warming caused by anthropogenic climate change is already starting to impact the marine biota, with possible consequences for ocean productivity and ecosystem services. Because temperature sensitivities of marine autotrophic and heterotrophic processes differ greatly, ocean warming is expected to cause major shifts in the flow of carbon and energy through the pelagic system. Attempts to integrate such biological responses into marine ecosystem and biogeochemical models suffer from a lack of empirical data. Here, we show, using an indoor-mesocosm approach, that rising temperature accelerates respiratory consumption of organic carbon relative to autotrophic production in a natural plankton community. Increasing temperature by 2-6°C hence decreased the biological drawdown of dissolved inorganic carbon in the surface layer by up to 31%. Moreover, warming shifted the partitioning between particulate and dissolved organic carbon toward an enhanced accumulation of dissolved compounds. In line with these findings, the loss of organic carbon through sinking was significantly reduced at elevated temperatures. The observed changes in biogenic carbon flow have the potential to reduce the transfer of primary produced organic matter to higher trophic levels, weaken the ocean's biological carbon pump, and hence provide a positive feedback to rising atmospheric CO 2.biological feedbacks ͉ carbon cycle ͉ climate change ͉ global warming ͉ marine T he ocean plays a dominant role in the climate system through storage and transport of heat (1) and by mitigating global warming through the uptake and sequestration of anthropogenic carbon dioxide (CO 2 ) (2). Over the past 40 years, Ϸ84% of the increase in the Earth's heat budget has been absorbed by the surface oceans (3), thereby increasing the average temperature of the upper 700 m by 0.1°C (4). This process is likely to accelerate in the next decades with a predicted increase in global mean surface temperature between 1.1°C (low CO 2 emission scenario B1) and 6.4°C (high CO 2 emission scenario A1FI) until the end of the 21st century (5).Sea surface warming will affect the pelagic ecosystem in 2 ways: directly through its effect on the rates of biological processes, and indirectly through decreased surface layer mixing, causing decreased nutrient supply and increased light availability for photosynthetic organisms suspended in the upper mixed layer. It is expected that these changes in the physical and chemical environment will have drastic effects on the marine biota. The sensitivity of biological processes to temperature is commonly described by the Q 10 factor, the factorial increase in the process rate for a 10°C increase in temperature. While phytoplankton growth and photosynthesis show only a moderate temperature-response (1 Ͻ Q 10 Ͻ 2) and are primari...

Elevated temperature alters proteomic responses of individual organisms within a biofilm community

“…Increasing temperatures have been shown to enhance the decomposition of organic matter and the extracellular release of carbohydrates in seawater (Wohlers et al, 2009;Engel et al, 2011). Here, 20 different CAZymes were quantified for Leptospirillum group III bacteria (Figure 4).…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…The exception to this trend was the prymnesiophyte Emiliana huxleyi, which showed no relationship between TEP production rate and temperature. There is evidence from mesocosm experiments for increased DOM release by natural phytoplankton grown at elevated temperature Wohlers et al, 2009). The C : N ratio of the DOM increased at a higher temperature due to increased production of dissolved carbohydrates .…”

Southern Ocean phytoplankton physiology in a changing climate

“…In addition, increases in ocean temperature coincide with a decline in the size of diatom frustules (Falkowski and Oliver, 2007) making them too small to be efficiently captured by krill and favouring their consumption by microheterotrophs such as ciliates (Boyd et al, 1984;Kawaguchi et al, 1999;Caron and Hutchins, 2013 and refs therein). The resultant shift in the SO trophodynamics toward grazing by microzooplankton would reduce the transfer of phytoplankton productivity to higher trophic levels, again favouring the respiration of carbon substrates in surface waters (Wohlers et al, 2006). Furthermore, the resulting decline in the efficiency of the biological pump would have a positive feedback on global climate change.…”