Organic Carbon In Surface Waters Research Articles

Composition and flux of particulate amino acids and chloropigments in equatorial Pacific seawater and sediments

Compositions and fluxes of amino acids and major chloropigments were measured in the central equatorial Pacific Ocean as part of the US JGOFS EqPac program. Fluxes decreased by several orders of magnitude, from 400 to 0.03 mg amino acid m −2 d −1 and from 9 mg to 0.0004 μg chloropigment m −2 d −1, between production in the surface waters and accumulation at the sea floor. Most rapid losses were in surface waters and at the sediment interface. Losses from the mid-water column were as great as those in surface waters or at the sediment interface, but occurred over a much greater depth range. Export flux estimates based on floating sediment traps were higher near the equator and decreased poleward, similar to primary production. Little meridional difference was apparent in composition of either amino acids or pigments in exported material over the 24° of latitude sampled in spite of the large (factor of 5–6) difference in fluxes. However, pigment composition changed dramatically with depth in the water column, and considerable diagenesis occurred before particles reached the sediment. Pigment compositions suggest that suspended particles were more degraded in the northern than in the southern hemisphere, possibly due to differences in food chain structure. Compositional changes in amino acids occurred in the water column, but were most noticeable at the sediment–seawater interface. Increases in the relative proportions of aspartic acid and glycine with depth were more consistent with preferential preservation within the particulate matrix than with any inherent stability of these compounds to heterotrophic consumption. The contribution of amino acids and pigments to total organic carbon clearly shows that selective degradation of organic matter occurs with depth; this is not evident from total organic carbon data alone. Amino acids contributed about a quarter of the total organic carbon (OC) in surface waters and 16% of the OC in sediment; pigments decreased from 1% of total OC in surface waters to <0.001% in sediments. Decreases in the contribution of amino acids to total organic carbon may be due to transformation into uncharacterizeable material as well as to respiration.

Suspended Particulate Organic Matter Concentration and Export in Streams

Suspended Particulate Organic Matter Concentration and Export in Streams

Variations in the isotopic composition of particulate organic carbon in surface waters along an 88°W transect from 67°S to 54°S

The concentration and isotopic composition of carbon was measured in suspended particulate organic matter in surface waters of the Southern Pacific Ocean along an 88°°W transect from 67−54°S during the Austral summer. Concurrent measurements of total dissolved inorganic carbon (ΣCO 2), pCO 2, particulate organic carbon (POC), salinity, chlorophyll and temperature provide an opportunity to study the covariance of these parameters with changes in the isotopic composition of particulate organic carbon (δ 13C-POC). The south-north transect did not show any significant changes in POC (10–19 mmol m −3) or chlorophyll (0.5–1 mg m −3), while δ 13C-POC variations of approximately 4%o were recorded. Although surface water CO 2(aq) is substantially out of equilibrium with the local atmosphere, the isotopic changes are negatively correlated with the concentration of dissolved carbon dioxide along the transect, and follow the general trends predicted from previously determined relationships. Estimates of ε p ( ε # p ) are less well constrained and show a weaker correlation with [CO 2 (aq)]. Where ε # p varies independently of [C0 2(aq)] small changes in the concentration gradient between extra- and intra-cellular CO 2 can be predicted. The difficulty in obtaining independent measures of growth rate and matching these measurements to the timescales over which the 613C of the phytoplankton is integrated is examined.

Carbon isotopes in recent planktonic foraminifera: A record of anthropogenic CO 2 invasion of the surface ocean

The release of isotopically light anthropogenic CO 2 into the ocean-atmosphere carbon reservoir has resulted in a decrease in the carbon isotopic composition of the surface ocean. In this paper we examine differences between the carbon isotope composition of planktonic foraminifera from sediment traps with older late Holocene material to estimate the change in δ 13C ( Δδ 13C) in Eastern Atlantic surface waters as a result of the invasion of anthropogenic CO 2. Using stable oxygen isotopes we demonstrate that average trap values for a variety of species are more or less identical to core-top values, suggesting that foraminifera recovered in sediment traps are representitive of foraminifera deposited in the sediments. However, carbon isotopes recorded in planktonic foraminifera from recent trap material reveal a decrease in the δ 13C composition of all species relative to the core-top samples, although the magnitude of the decrease varies significantly between species. Surface-dwelling foraminifera ( G. ruber, G. bulloides) show Δδ 13C values of −0.53‰ to −0.62‰, which is similar to other estimates from shallow water coral and sponge records for the decrease in the δ 13C composition of dissolved organic carbon in surface waters which has taken place since the start of the anthropogenic emissions. The magnitude of decrease in the δ 13C of surface waters suggested by these records is also close to that predicted by global carbon cycle models. Deeper, thermocline dwelling foraminifera such as G. inflata however, show Δδ 13C values (0.2‰) which are substantially lower than their surface-dwelling counterparts. This reduction in Δδ 13C with increasing depth habitat within the mixed layer may be related to limited vertical penetration of anthropogenic CO 2 as a result of the strong upwelling which is observed in the Eastern Atlantic along the Northwest African margin.

A high-temperature catalytic oxidation method for the determination of non-volatile dissolved organic carbon in seawater by direct injection of a liquid sample

A method is described for the rapid, precise determination of non-volatile dissolved organic carbon in seawater in concentrations between 0 and 2000 μM. The oxidation is carried out on a platinum catalyst at 680 °C under an oxygen atmosphere after the sample has been freed of inorganic carbon, and the concentration of the CO 2 generated is measured with a non-dispersive IR gas analyzer. The determination can be carried out on board ship with a precision of ±2% using a sample volume of 200 μl. The results obtained using this method are of a much higher value than those obtained using persulfate oxidation methods. The molecular weight dependency of the results clearly indiates that the above discrepancy is caused by the low oxidation efficiency of the persulfate oxidation method against high-polymer organic matter dissolved in seawater. The results reveal that the concentration of dissolved organic carbon in surface water is about 300 μM and decreases with depth. An examination of molecular weight distribution indicates that the concentration of high-polymer organic carbon decreases rapidly from surface to deeper layers, with molecular weight ranging from 1.8 x 10 3 to 6 x 10 4 Dalton. It is noted that there is an inverse correlation between the concentration of dissolved organic carbon and apparent oxygen utilization (AOU). Frozen or acidified preservation of unfiltered samples does not give reliable results. An essential requirement for dissolved carbon analysis is membrane filtration just after sampling and real-time analysis on board. Because of the well-defined principle of the oxidation process, its reliability, the ease of sample handling and of the analytical procedure on board or in the land laboratory, and the consistency of the oceanographic parameters, this method is much more suitable for the analysis of marine dissolved organic carbon than the methods used previously.

Stable isotope ratios of particulate organic carbon in surface water at inner part of Tokyo Bay

Stable isotope ratios of particulate organic carbon in surface water at inner part of Tokyo Bay

The relation of fluorescence to dissolved organic carbon in surface waters : SMART P. L., B. L. FINLAYSON, W. D. RYLANDS and C. M. BALL, 1976 Wat. Res., 10 (9): 805–811

The relation of fluorescence to dissolved organic carbon in surface waters : SMART P. L., B. L. FINLAYSON, W. D. RYLANDS and C. M. BALL, 1976 Wat. Res., 10 (9): 805–811

The relation of fluorescence to dissolved organic carbon in surface waters

A rapid method for the estimation of organic carbon in natural waters which could be adapted to continuous measurement is needed to improve water quality monitoring. The fluorescent properties of natural organic molecules offer such a method. The fluorescence of natural waters from a variety of surface sources, using an excitation wavelength of 365 nm and emission wavelengths in the range 400–600 nm have been correlated with total organic carbon levels. The results are highly significant statistically and show that fluorescence can be used as a predictor of TOC over a wide range of concentrations.

ORGANIC AGGREGATES IN SURFACE AND DEEP WATERS OF THE SARGASSO SEA1

The quantities of organic aggregates and particulate organic carbon in surface waters of the Sargasso Sea were relatively small at all times but showed a slight seasonal variation, with highest values in winter and spring and lower ones in summer, in general agreement with observed seasonal variations in phytoplankton. Particulate matter decreased from the surface downward in the upper few hundred meters but was essentially constant from 500 m to more than 3,000 m. It is concluded that: a) There are bacteria and filter‐feeding animals in deep water which are potentially able to use this particulate matter. b) The particulate matter is large in total quantity but too thinly distributed to provide more than a minimal diet; hence the quantity of animals is small, and the turnover rate of organic matter is slow. c) Biological consumption in deep water should produce a decrease in organic matter with depth, unless this particulate matter is augmented by additional adsorption from the dissolved organic fraction. Preliminary experiments confirm the adsorption process as a possible explanation of observed distributions.