Multiple stressors of ocean ecosystems in the 21st century: projections with CMIP5 models

Abstract

Ocean ecosystems are increasingly stressed by human-induced changes of their physical, chemical and biological environment. Among these changes, warming, acidification, deoxygenation and changes in primary productivity by marine phytoplankton can be considered as four of the major stressors of open ocean ecosystems. Due to rising atmospheric CO<sub>2</sub> in the coming decades, these changes will be amplified. Here, we use the most recent simulations performed in the framework of the Coupled Model Intercomparison Project 5 to assess how these stressors may evolve over the course of the 21st century. The 10 Earth System Models used here project similar trends in ocean warming, acidification, deoxygenation and reduced primary productivity for each of the IPCC's representative concentration parthways (RCP) over the 21st century. For the "business-as-usual" scenario RCP8.5, the model-mean changes in 2090s (compared to 1990s) for sea surface temperature, sea surface pH, global O<sub>2</sub> content and integrated primary productivity amount to +2.73 °C, −0.33 pH unit, −3.45% and −8.6%, respectively. For the high mitigation scenario RCP2.6, corresponding changes are +0.71 °C, −0.07 pH unit, −1.81% and −2.0% respectively, illustrating the effectiveness of extreme mitigation strategies. Although these stressors operate globally, they display distinct regional patterns. Large decreases in O<sub>2</sub> and in pH are simulated in global ocean intermediate and mode waters, whereas large reductions in primary production are simulated in the tropics and in the North Atlantic. Although temperature and pH projections are robust across models, the same does not hold for projections of sub-surface O<sub>2</sub> concentrations in the tropics and global and regional changes in net primary productivity

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

“…Our findings imply that if, due to climate change, present habitats for larval krill overwintering and nursery in the South Scotia Ridge and southern Scotia Sea 1 become ice free in winter, there may be an increase in food for larval krill development and growth [32][33][34][35][36][37] . If, however, the seasonal sea-ice cover does not extend as far north in future, then larvae that are released from under the sea ice in spring will be farther south in the Weddell Sea (south of the South Scotia Ridge in spring) and will take longer to reach the Scotia Sea 17 ( Supplementary Fig.…”

Winners and losers: Ecological and biogeochemical changes in a warming ocean

“…Locally, there are only select regions of general agreement between models, with other regions of disparate signs of changes [Bopp et al, 2013]. On the other hand, most numerical projections agree on the sign of the change in globally integrated export production, with better regional agreement as well.…”

“…[4] Published numerical projections of future oceans suggest very different changes in global integrated primary production in future scenarios [Sarmiento et al, 2004;Schmittner et al, 2008;Steinacher et al, 2010;Marinov et al, 2010;Taucher and Oschlies, 2011;Bopp et al, 2005;Bopp et al, 2013], even disagreeing on the sign of the net change. Locally, there are only select regions of general agreement between models, with other regions of disparate signs of changes [Bopp et al, 2013].…”

Spatiotemporal Assessment of CO2–Carbonic Acid System Dynamics in a Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern Hawaiian Islands

“…Coral reefs experience high rates of metabolic activity and calcification is influenced by hydrodynamics (e.g., circulation), geomorphology, light, temperature, nutrients and benthic composition (Grigg 1982;Bates et al 2001;Suzuki and Kawahata 2003;Anthony et al 2011;Albright et al 2013;Falter et al 2013). Furthermore, the complex coupling between physical, chemical and biological dynamics can drive changes in the CO 2 -carbonic acid system over a diel cycle that are greater than the magnitude of change predicted by the year 2100 (Hofmann et al 2011;Bopp et al 2013). Hence, distinguishing between natural variability and anthropogenically driven changes is difficult.…”

“…OA refers to the oceanic absorption of anthropogenic carbon dioxide (CO 2 ) and the consequent decline in ocean pH (Caldeira and Wickett 2003;Feely et al 2004). Under the 'business as usual'' scenario RCP8.5, average open ocean surface seawater pH is expected to decline 0.33 units by the end of the twenty-first century (Bopp et al 2013), andvan Hooidonk et al (2014) suggest that calcification at all reef locations worldwide will decline by 5% by the year 2034.…”