Description: Throughout the transition from the last Glacial to the current Interglacial, rising atmospheric CO2 levels were accompanied by declining atmospheric Δ14C values. A likely mechanism, influencing both components is the deglacial release of CO2, stored for millennia in the deep Ocean, to the atmosphere. Due to its long residence time within the oceans interior this CO2 rich water mass was considerably depleted in radiocarbon. Although a large number of studies address this topic, the extent, location and pathways of the glacial carbon pool are still subjects of an ongoing debate. As deep water masses are upwelled and new intermediate waters are formed around Antarctica, the Southern Ocean is a potential area for the deglacial release of stored CO2. Here we present radiocarbon and carbonate ion data from a transect of sediment cores off New Zealand that covers the major water masses in this area, from the AAIW down to the AABW. During the Glacial, our data locate a significantly 14C depleted pool in a water depth between 2000 and 4500 m. The combination of Δ14C and [CO32-] records provides new insights into the process of oceanic-atmospheric CO2 exchange in the Southern Ocean. In addition, our results yield new implications for contradicting Δ14C records from the Southern Ocean and lower latitudes.

Description: Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 173 (2016): 64-85, doi:10.1016/j.gca.2015.10.021.

Description: Hydrothermal vent deposits form on the seafloor as a result of cooling and mixing of hot hydrothermal fluids with cold seawater. Amongst the major sulfide and sulfate minerals that are preserved at vent sites, barite (BaSO4) is unique because it requires the direct mixing of Ba-rich hydrothermal fluid with sulfate-rich seawater in order for precipitation to occur. Because of its extremely low solubility, barite crystals preserve geochemical fingerprints associated with conditions of formation. Here, we present data from petrographic and geochemical analyses of hydrothermal barite from the Endeavour Segment of the Juan de Fuca Ridge, northeast Pacific Ocean, in order to determine the physical and chemical conditions under which barite precipitates within seafloor hydrothermal vent systems. Petrographic analyses of 22 barite-rich samples show a range of barite crystal morphologies: dendritic and acicular barite forms near the exterior vent walls, whereas larger bladed and tabular crystals occur within the interior of chimneys. A two component mixing model based on Sr concentrations and 87Sr/86Sr of both seawater and hydrothermal fluid, combined with 87Sr/86Sr data from whole rock and laser-ablation ICP-MS analyses of barite crystals indicate that barite precipitates from mixtures containing as low as 17% and as high as 88% hydrothermal fluid component, relative to seawater. Geochemical modelling of the relationship between aqueous species concentrations and degree of fluid mixing indicates that Ba2+ availability is the dominant control on mineral saturation. Observations combined with model results support that dendritic barite forms from fluids of less than 40% hydrothermal component and with a saturation index greater than ~0.6, whereas more euhedral crystals form at lower levels of supersaturation associated with greater contributions of hydrothermal fluid. Fluid inclusions within barite indicate formation temperatures of between ~120 and 240°C during barite crystallization. The comparison of fluid inclusion formation temperatures to modelled mixing temperatures indicates that conductive cooling of the vent fluid accounts for 60 – 120°C reduction in fluid temperature. Strontium zonation within individual barite crystals records fluctuations in the amount of conductive cooling within chimney walls that may result from cyclical oscillations in hydrothermal fluid flux. Barite chemistry and morphology can be used as a reliable indicator for past conditions of mineralization within both extinct seafloor hydrothermal deposits and ancient land-based volcanogenic massive sulfide deposits.

Description: This work was supported by an NSERC PGS scholarship to JWJ and NSERC Discovery Grant to MDH. MKT acknowledges funding from NSF OCE- 1130019. DAB acknowledges funding from NSF OCE-0731947 and the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA10OAR4320148.

Description: The transfer of vast amounts of carbon from a deep oceanic reservoir to the atmosphere is considered to be a dominant driver of the deglacial rise in atmospheric CO2. Paleoceanographic reconstructions reveal evidence for the existence of CO2-rich waters in the mid to deep Southern Ocean. These water masses ventilate to the atmosphere south of the Polar Front, releasing CO2 prior to the formation and subduction of intermediate-waters. Changes in the amount of CO2 in the sea water directly affect the oceanic carbon chemistry system. Here we present B/Ca ratios, a proxy for delta carbonate ion concentrations Δ[CO32−], and stable isotopes (δ13C) from benthic foraminifera from a sediment core bathed in Antarctic Intermediate Water (AAIW), offshore New Zealand in the Southwest Pacific. We find two transient intervals of rising [CO32−] and δ13C that that are consistent with the release of CO2 via the Southern Ocean. These intervals coincide with the two pulses in rising atmospheric CO2at ~ 17.5–14.3 ka and 12.9–11.1 ka. Our results lend support for the release of sequestered CO2 from the deep ocean to surface and atmospheric reservoirs during the last deglaciation, although further work is required to pin down the detailed carbon transfer pathways.