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Dissolved organic matter (DOM) absorbance and fluorescence were used as optical proxies to track terrestrial DOM fluxes through estuaries and coastal waters by comparing models developed for several coastal ecosystems. Key to using these optical properties is validating and calibrating them with chemical measurements, such as lignin-derived phenols-a proxy to quantify terrestrial DOM. Utilizing parallel factor analysis (PARAFAC), and comparing models statistically using the OpenFluor database (http://www.openfluor.org) we have found common, ubiquitous fluorescing components which correlate most strongly with lignin phenol concentrations in several estuarine and coastal environments. Optical proxies for lignin were computed for the following regions: Mackenzie River Estuary, Atchafalaya River Estuary (ARE), Charleston Harbor, Chesapeake Bay, and Neuse River Estuary (NRE) (all in North America). The slope of linear regression models relating CDOM absorption at 350 nm (a350) to DOC and to lignin, varied 5-10-fold among systems. Where seasonal observations were available from a region, there were distinct seasonal differences in equation parameters for these optical proxies. The variability appeared to be due primarily to river flow into these estuaries and secondarily to biogeochemical cycling of DOM within them. Despite the variability, overall models using single linear regression were developed that related dissolved organic carbon (DOC) concentration to CDOM (DOC = 40 ± 2 × a350 + 138 ± 16; R2 = 0.77; N = 130) and lignin (Σ8) to CDOM (Σ8 = 2.03 ± 0.07 × a350 - 0.47 ± 0.59; R2 = 0.87; N = 130). This wide variability suggested that local or regional optical models should be developed for predicting terrestrial DOM flux into coastal oceans and taken into account when upscaling to remote sensing observations and calibrations.

As human activities have intensified along tropical coastlines, the anthropic influence on adjacent coral reefs has become increasingly deleterious. Changes in land use generally degrade water quality, but controversy persists over the degree to which reduced water quality affects the ecology of reef communities. We cored reef frameworks at 4 sites in Bahía Almirante, a semi-enclosed, coastal lagoon in northwestern Panamá, to explore the historical relationship between turnover in coral-species dominance and terrigenous input. The coral constituents of the cores were analyzed in tandem with lignin-phenol concentrations. Chronologies and sedimentation rates were determined from 210Pb profiles in the cores. Increased terrigenous input from agricultural development and expansion of the human population degraded water quality in Bahía Almirante over the last century. Documented episodes of heavy rainfall after 1970 accelerated a phase shift from dominance by branching corals of the genus Porites to dominance by the lettuce coral Agaricia tenuifolia at water depths of 5 to 10 m by increasing runoff, increasing sediment and nutrient loads, and lowering light levels. The phase shift in coral dominance was unprecedented on a millennial time scale and the degree to which it occurred varied along a gradient of terrigenous input to the Bahía.

Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3–4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0–1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the “true” (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.

The carbon cycle of the coastal ocean is a dynamic component of the global carbon budget. But the diverse sources and sinks of carbon and their complex interactions in these waters remain poorly understood. Here we discuss the sources, exchanges and fates of carbon in the coastal ocean and how anthropogenic activities have altered the carbon cycle. Recent evidence suggests that the coastal ocean may have become a net sink for atmospheric carbon dioxide during post-industrial times. Continued human pressures in coastal zones will probably have an important impact on the future evolution of the coastal ocean's carbon budget.

Seabed cores collected on the continental shelf adjacent to the Mississippi River show a direct temporal correlation between decreases in mass accumulation rate (factor of 2-3) and suspended sediment loads in the river. This mid 20th century decline is not apparent shelf-wide due to sediment focusing and biological seabed mixing. Total organic carbon diagenetic loss rate across this sediment age interval is relatively uninterrupted when coffected for the non-steady state mass flux. This suggests that organic carbon burial rates in oxic bottom water settings on river-dominated continental margins are directly proportional to lithogenic flux. Variations in OM remineralization rates due to changes in the composition (marine vs. terrestrial) of the particulate OM flux at the sediment surface are a second-order effect that cannot be distinguished in the bulk carbon sediment record at these oxic sites; although they may significantly alter the OM degradation-induced CO2 flux to the overlying water column.