Does sea level influence mid-ocean ridge magmatism on Milankovitch timescales?

Abstract

Magma production at mid-ocean ridges is driven by seafloor spreading and decompression melting of the upper mantle. In the special case of Iceland, mantle melting may have been amplified by ice sheet retreat during the last deglaciation, yielding anomalously high rates of subaerial volcanism. For the remainder of the global mid-ocean ridge system, the ocean may play an analogous role, with lowering of sea level during glacial maxima producing greater magma flux to ridge crests. Here we show that the mantle decompression rate associated with changes in sea level is a substantial fraction of that from plate spreading. Modeled peaks in magma flux occur after sea level drops rapidly, including the Marine Isotope Stage (MIS) 5/4 and 3/2 transitions. The minimum in simulated flux occurs during the mid-Holocene, due to the rapid sea level rise at the MIS 2/1 boundary. The model results are highly sensitive to melt migration rate; rates of ~1 m/yr produce small signals, while those >5 m/yr yield substantial anomalies. In the latter case, sea level-driven magma flux varies by 15–100% relative to the long-term average, with the largest effect occurring at slow-spreading ridges. We suggest that sedimentary time series of hydrothermal particle flux, oceanic Os isotopic ratio, and oceanic radiocarbon may serve as proxies for magma-flux variations at mid-ocean ridges. Although well-dated records are rare, preliminary data from the Pacific and Atlantic suggest hydrothermal metal flux was elevated during MIS 2 and 4, broadly consistent with our modeling results.

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