Orbital forcing of deep-sea benthic species diversity

Abstract

Explanations for the temporal and spatial patterns of species biodiversity focus on stability–time1–3, disturbance–mosaic (biogenie microhabitat heterogeneity)4,5 and competition–predation (biotic interactions)6,7 hypotheses. The stability–time hypothesis holds that high species diversity in the deep sea and in the tropics reflects long-term climatic stability3. But the influence of climate change on deep-sea diversity has not been studied and recent evidence suggests that deep-sea environments undergo changes in climatically driven temperature8 and flux of nutrients9 and organic-carbon10 during glacial–interglacial cycles. Here we show that Pliocene (2.85–2.40 Myr) deep-sea North Atlantic benthic ostracod (Crustacea) species diversity is related to solar insolation changes caused by 41,000-yr cycles of Earth's obliquity (tilt). Temporal changes in diversity, as measured by the Shannon–Weiner index, H(S), correlate with independent climate indicators of benthic foraminiferal oxygen-isotope ratios (mainly ice volume11–13) and ostracod Mg:Ca ratios (bottom-water temperature8). During glacial periods, H(S) = 0.2–0.6, whereas during interglacials, H(S) = 1.2–1.6, which is three to four times as high. The control of deep-sea benthic diversity by cyclic climate change at timescales of 103–104 yr does not support the stability–time hypothesis because it shows that the deep sea is a temporally dynamic environment. Diversity oscillations reflect large-scale response of the benthic community to climatically driven changes in either thermohaline circulation, bottom temperature (or temperature-related factors) and food, and a coupling of benthic diversity to surface productivity.