Glacial/interglacial control of terrigenous and biogenic fluxes in the deep ocean off a high input, collisional margin: A 139 kyr-record from New Zealand

Sediment input to the deep ocean, off the New Zealand collisional plate boundary, is large and variable as revealed by a 139 kyr-old record from the 34.92 m-long core, MD97 2121. Mass accumulation rates (MARs) were derived for terrigenous and biogenic (carbonate and silica) sedimentary components, with temporal control from a stable isotope age model verified by tephra and radiocarbon ages. Terrigenous MARs changed in phase with glacio-eustatic fluctuations of sea level. Highest rates (≥ 30 g/cm2/kyr) coincided with the late regressive-lowstand-early transgressive phase of marine isotope stage (MIS) 2 when rivers discharged at or near the shelf edge. Lesser, but still high terrigenous rates (20–30 g/cm2/kyr) characterized peak warm phases of early MIS 5 and 1, when a strengthened Subtropical Inflow probably introduced sediment from fluvial and seabed sources to the north of MD97 2121. However, during prolonged highstands the flux declined as more sediment was retained on a tectonically subsiding shelf with a shore-parallel current. Paradoxically, the lowest MARs (10–5 g/cm2/kyr) occurred in MIS 4; either sea level was too high to allow much sediment to escape off-shelf, or the fluvial input was modest, or both these factors. e the terrigenous dominance, biogenic MARs are high, and are 2–4 times larger than SW Pacific Ocean rates. MARs were lowest during MIS 4 and 3, possibly due to reduced marine production under a lowered input of fluvial micronutrients. In contrast, MARs increased irregularly though glacial maxima to peak at 5–6 g/cm2/kyr carbonate and 2–2.5 g/cm2/kyr silica in early-mid MIS 5 and 1. Such rates reflected the interaction of macronutrient-rich subantarctic waters, sourced from the south, with local, micronutrient-rich subtropical waters. Production also responded to warmer temperatures, elevated nutrient runoff and a more stratified surface ocean. Later in MIS 5 and 1, fluxes reduced as less productive subtropical waters prevailed. That biogenic and aeolian MAR profiles are out of phase, suggests Fe-fertilization by aerosolic dust was not a major influence.