Glacial to interglacial changes in non-carbonate and carbonate accumulation in the SW Pacific Ocean, New Zealand

Abstract

Fluxes of carbonate and non-carbonate (terrigenous+biogenic siliceous) sediment, back to a maximum of marine isotope stage (MIS) 6, were determined for 54 cores from off eastern New Zealand. Mass accumulation rates (MARs) were derived using dry bulk densities measured directly from fresh cores or, in the case of dry archived samples, on estimates from a density/carbonate relationship.MARs exhibit wide spatial and temporal variability in response to (i) the location of cores relative to the terrigenous source of New Zealand, current pathways and local oceanographic features, and (ii) palaeoclimatic change. For MIS 1–2, non-carbonate accumulated at a high rate between 27 and 18 ka (calendar years), due to an influx of waterborne and aeolian terrigenous detritus together with localised production of biogenic silica under a northward intrusion of subantarctic waters, and an increase in wind-induced upwelling. By 18–12 ka, non-carbonate MARs reduced as winds ameliorated and sea level rose to confine some of the terrigenous load to the continental shelf. The Holocene transgression was accompanied by warmer sea surface temperatures, the formation of coastal and lacustrine sediment traps, and more widespread terrestrial vegetation. These conditions further reduced the deep oceanic non-carbonate flux to levels about half those of glacial periods.In contrast, carbonate MARs were lower in cold periods, reflecting lower productivity, increased dissolution and, in the case of the generally productive waters of Chatham Rise, to redistribution by bottom currents. However, off central New Zealand, carbonate production was higher on the continental margin, possibly because of enhanced upwelling under the strong wind regime of MIS 2. Such localised effects produced glacial carbonate MARs higher than interglacial MIS 1 values. For the rest of the region, carbonate fluxes increased to an early to middle MIS 1 maximum before generally declining in recent times.