Physical oceanography during VALDIVIA cruise VA154

University of Hamburg, Department of Chemistry. Authorship was originally "OMEX Project Members; BODC" and was changed by request of the BODC

Separation of natural organic colloids with a PALL tangential flow filtration system

The applicability of a PALL tangential flow filtration (TFF) system for size fractionation of natural dissolved organic matter was investigated. The performance of polyethersulfone membranes with nominal molecular weight cut-off of 1 kDa, 5 kDa and 50 kDa was examined for isolation of low and high molecular weight compounds in fresh and estuarine waters with diverse physico-chemical properties. Detailed protocols for operating the TFF- system and for membrane cleaning are proposed. The ultrafiltration membranes can be efficiently cleaned to provide low carbon blanks (&amp;lt;0.09 mg/l). Standard colloid tests confirmed that the higher molecular weight compounds were isolated in the retentate and the lower molecular weight compounds remain in the permeate. Mass balance of fractionated natural samples showed good recoveries for dissolved organic carbon (DOC) (99±13% (1 kDa); 103±20% (5 kDa); 94±14% (50 kDa) (n=9). Moreover, high ionic strength or high DOC content did not enhance either fouling or contamination of the membrane. These findings demonstrate that the PALL TFF system is reliable for natural organic colloids fractionation in aquatic systems across both salinity and DOC gradients.</jats:p

Physical oceanography during POSEIDON cruise POS219A/2

Physical oceanography during POSEIDON cruise POS219A/

(Table 7) Vitrinite reflectance at DSDP Hole 93-603B

Sediment depth is given in mbsf. # = Sample 93-603B-36-3, 40 cm is a claystone subsample low in Corg > from 93-603B-36-3, 30-40 cm

Carbon and oxygen budget in the deep, strongly stratified Congo River Estuary

The Congo River region of freshwater influence (ROFI) is characterized by a deep canyon that connects the river to the deep ocean by cutting through the continental shelf (Shepard & Emery, 1973). In the estuary, high discharge of freshwater and very small vertical mixing within the canyon restricts the supply of oxygen from the surface waters to the more saline bottom waters, where the remineralisation of riverine particulate organic carbon leads to hypoxia (Eisma & Van Bennekom, 1978). We study the dynamics of the Congo River ROFI by applying the multi-scale baroclinic coastal ocean model SLIM 3D (www.slim-ocean.be) to this challenging environment. Model results compare favourably against in-situ observation in the estuary, suggesting that the exchange flow is correctly simulated. Using water ages as a diagnostic tool allows gaining deeper insight into the fate of riverine and oceanic water. We use the simulated renewing time of the canyon’s water body by oceanic water (R = 20 d) to calculate an oxygen and carbon budget of the subhalocline water body from the remineralization of POC. The renewing oceanic waters originate from the Eastern Atlantic equatorial oxygen minimum zone. At a representative station in the canyon 60 km offshore the oxygen concentration was measured as 0,05 – 0,1 [mol O2/m3] at water depths of 200 - 500 [m]. Following Eisma & Kalf (1984) we split the recent Congo River POC flux of 5260 [mol C s-1] (Coynel et al., 2005) into 50 % settling into the subhalocline water body, the other 50 % being advected offshore with the surface plume. Given these assumptions for the oxygen and carbon boundary fluxes, only 15 % of the settling POC are remineralised by aerobic degradation within the canyon, confirming oxygen limitation and leaving a substantial fraction of available labile POC undegraded (generally 35 % of tropical riverine POC are labile; Ittekkot, 1988). Summing up, the canyon’s oxygen balance is ocean oxygen- rather than river POC - controlled, and scenarios of even substantial future POC-flux reductions by land use change and/or reservoir construction within the catchment should therefore not imply significant changes in the Congo River estuarie’s oxygen balance

(Table 5) Dissolved organic carbon in interstitial water at DSDP Holes 93-603 and 93-603B

(Table 5) Dissolved organic carbon in interstitial water at DSDP Holes 93-603 and 93-603