Temperature-Metabolism Linkage and the Effects on Marine Biota: Evidence Across the Middle Eocene Climatic Optimum in the South-East Atlantic

Abstract:

The Middle Eocene Climatic Optimum (MECO; ~40 Ma) stands out as a middle-term (~500 kyr) interval of warming, interrupting the long-term cooling starting in the latest early Eocene.To characterize oceanographic and biotic changes related to the MECO, we performed a multiproxy investigation at Site 1263 (Walvis Ridge; 28°31.98′S, 02°46.77′E, 2 Km paleodepth), which has a continuous record, not affected by carbonate dissolution. We coupled surface to bottom oxygen and carbon stable isotopes, TEX₈₆, and biotic records from biomarker and micropaleontological analysis to first document both MECO climate change and its effects in an open ocean, SE Atlantic setting. Benthic foraminiferal, coarse fraction and fine fraction accumulation rates were used as proxies for benthic, planktic foraminiferal and nannoplankton productivity, and the abundance of crenarchaeol, biomarker of widespread archaeal nitrifiers, to infer ammonia utilization rates. Our records show an uniform, surface-to-deep warming during MECO at mid southern latitudes. In parallel, benthic and planktic foraminiferal productivity decreased markedly, whereas rates of ammonia consumption increased, while primary productivity and water column stratification appear unchanged. We ascribe these biotic changes to MECO warming, due to the temperature-dependency of metabolic rates, particularly of heterotrophic respirators (e.g., O’Connor et al., 2009). Increased oceanic temperature would have altered pelagic food webs, increasing heterotrophs metabolic rates, thus food needs. Therefore planktic foraminiferal populations declined, and organic matter remineralization in the water-column, i.e., ammonia production, increased. The carbon flux to the sea-floor decreased, starving benthic foraminifera. A decrease in organic carbon export and burial, if widespread in oligotrophic open-ocean areas, would have been important to sustain pCO₂rise during the early phase of MECO.

References:

O’Connor et al., 2009. PLoSBiol, doi:10.1371/journal.pbio.1000178