Benthic Oxygen Fluxes Research Articles

In situ measurements of calcium carbonate dissolution rates in deep-sea sediments

Benthic fluxes of alkalinity, carbon dioxide, and oxygen have been measured using an in situ incubation chamber at three sites (MANOP Sites C and S and PACFLUX Site SC) in the central equatorial north Pacific. At two carbonate-rich sites (C and SC), a budget for oxygen, alkalinity, and TCO 2 fluxes indicate a net CaCO 3 dissolution rate of approximately 0.4 mmol m −2 day −1. This rate is only 20% of previous estimates but is consistent with a dissolution rate constant predicted from laboratory experiments with deep-sea sediments and derived from in situ flux measurements in sediments of the southern California borderland. Organic matter oxidation in the sediment column provides the acid for 60–100% of the calcium carbonate dissolution occurring at these sites with the remainder derived from undersaturated bottom water. At a low-carbonate site (S), no carbonate dissolution in the sediment or on the sea floor is apparent, although sediment traps indicate a rain of CaCO 3 through 3400 m. The rates of remineralization relative to resuspension or erosion at this site must differ for organic carbon and calcium carbonate, so that carbonate grains reaching the sea floor are physically removed by erosion or resuspension before they dissolve, while organic carbon is largely oxidized before it can be physically removed.

An in situ microprofiling instrument for measuring interfacial pore water gradients: methods and oxygen profiles from the North Pacific Ocean

An in situ microprofiling instrument has been developed to study the composition of pore waters at the interface of deep-ocean sediments. The device lowers and operates microelectrodes. It has been deployed by free vehicle, at four North Pacific Ocean sites spanning water depths of 1275–5790 m. Oxygen profiles with a vertical resolution of 1 mm, are reported from these deployments. Benthic oxygen fluxes calculated from the in situ gradients range from 0.04 ± 0.02 to 0.14 ± 0.04 μmol cm −2 day −1. Microelectrode oxygen measurements in box-cored sediments never precisely duplicated the in situ distributions, especially near the sediment-water interface, where definition of the gradient is most critical to flux determinations.

The calibration of a new free-vehicle benthic flux chamber for use in the deep sea

A new free-vehicle benthic lander has been developed, capable of measuring benthic fluxes of nutrients, alkalinity, oxygen and radon. Important features of the device are the capability to collect sequential samples of 200 ml or more from three flux chambers, the ease of deployment, and the low cost. It has been tested in two basins of the California Borderland. Radon fluxes measured in these basins are consistent with those obtained by integrating the standing crop in the water column. Measurements of oxygen and nitrate uptake by these sediments are not strongly dependent on the rate of stirring within the lander flux chambers.