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

Abstract

[1] We employ a marine ecosystem model, with diverse and flexible phytoplankton communities, coupled to an Earth system model of intermediate complexity to explore mechanisms that will alter the biogeography and productivity of phytoplankton populations in a warming world. Simple theoretical frameworks and sensitivity experiments reveal that ecological and biogeochemical changes are driven by a balance between two impacts of a warming climate: higher metabolic rates (the "direct" effect), and changes in the supply of limiting nutrients and altered light environments (the "indirect" effect). On globally integrated productivity, the two effects compensate to a large degree. Regionally, the competition between effects is more complicated; patterns of productivity changes are different between high and low latitudes and are also regulated by how the supply of the limiting nutrient changes. These complex regional patterns are also found in the changes to broad phytoplankton functional groups. On the finer ecological scale of diversity within functional groups, we find that ranges of some phytoplankton types are reduced, while those of others (potentially minor players in the present ocean) expand. Combined change in areal extent of range and in regionally available nutrients leads to global "winners and losers." The model suggests that the strongest and most robust signal of the warming ocean is likely to be the large turnover in local phytoplankton community composition.

Time of emergence of trends in ocean biogeochemistry

“…The carbon cycle and the physical climate system strongly interact with each other (Joos et al, 1999), as illustrated by the manifold impacts of climate change on the global oceans. In addition to sea-level rise and ocean warming (e.g., Hegerl et al, 2007;Levermann et al, 2013;Dutkiewicz et al, 2013), we observe and model carbon-cycle related ocean acidification ) and deoxygenation Keeling et al, 2010). Consequently, a sound knowledge of the joint processes is a necessity not only for the correct detection of past and present trends, but also for robust projections of the future.…”

Drift in ocean currents impacts intergenerational microbial exposure to temperature

“…Until now, our understanding of how microbial communities will be reorganized under contemporary ocean change has developed from empirical studies involving examination of the current geographic distribution of microbial taxa and their relationships with temperature and other environmental parameters (8,10,13), laboratory investigations that measure performance of microbial ecotypes (thought to be representative of populations) under different conditions (6,7,9,14), and modeling studies that use microbial traits describing resource (e.g., nutrients, light) utilization to estimate fitness and predict future distributions of microbes under projected ocean change (15)(16)(17). The limitation of these studies is that microbial traits are assumed to be constant during model runs, so the microbes themselves are not responding to changes in their environment (18).…”

Phytoplankton adapt to changing ocean environments

“…If dispersal rates are rapid relative to the rate of evolutionary adaptation, changes in climate will result in local species being displaced by nonresident species from a regional pool of species that are better adapted to the new conditions (13). When modelers project changes in biotic communities under climate change scenarios, they generally assume that each species has a genetically determined fixed environmental niche and that species' spatial and temporal distributions will be determined by environmental conditions (14)(15)(16)(17). A recent model of this type predicts a loss of a third of tropical phytoplankton strains by 2100 with a ∼2°C increase in mean temperature (11); however, paleoecological studies indicate organisms may be much more resilient to climate change than these types of models suggest (18,19).…”