Adina Paytan

Glacial to Interglacial Fluctuations in Productivity in the Equatorial Pacific as Indicated by Marine Barite

An empirical correlation between marine barite (BaSO4) accumulation rate in core-top sediment samples from two equatorial Pacific transects (at 140°W and 110°W) and the estimated primary productivity of the overlying water column were used to evaluate glacial to interglacial changes in productivity. Fluctuations in barite accumulation rates down-core indicate that during glacial periods of the past 450,000 years, the productivity in the central and eastern equatorial Pacific was about two times that during intervening interglacial periods. This result is consistent with other evidence that productivity was high in the eastern and central equatorial Pacific during the last glacial.

Toxicity of atmospheric aerosols on marine phytoplankton

Atmospheric aerosol deposition is an important source of nutrients and trace metals to the open ocean that can enhance ocean productivity and carbon sequestration and thus influence atmospheric carbon dioxide concentrations and climate. Using aerosol samples from different back trajectories in incubation experiments with natural communities, we demonstrate that the response of phytoplankton growth to aerosol additions depends on specific components in aerosols and differs across phytoplankton species. Aerosol additions enhanced growth by releasing nitrogen and phosphorus, but not all aerosols stimulated growth. Toxic effects were observed with some aerosols, where the toxicity affected picoeukaryotes and Synechococcus but not Prochlorococcus. We suggest that the toxicity could be due to high copper concentrations in these aerosols and support this by laboratory copper toxicity tests preformed with Synechococcus cultures. However, it is possible that other elements present in the aerosols or unknown synergistic effects between these elements could have also contributed to the toxic effect. Anthropogenic emissions are increasing atmospheric copper deposition sharply, and based on coupled atmosphere–ocean calculations, we show that this deposition can potentially alter patterns of marine primary production and community structure in high aerosol, low chlorophyll areas, particularly in the Bay of Bengal and downwind of South and East Asia.

Origin of marine barite deposits: Sr and S isotope characterization

Barite can precipitate in microenvironments in the water column (marine barite), from supersaturated pore fluids at the oxic-anoxic boundary within marine sediments and where Ba-rich pore fluids are expelled and come into contact with sulfate-rich seawater (diagenetic barite), or from hydrothermal solutions (hydrothermal barite). Barite is relatively resistant to alteration after burial and has been used in paleoceanographic studies to reconstruct seawater chemistry and productivity through time. For such applications it is very important to determine the origin of the barite used, because both diagenetic and hydrothermal barite deposits may not accurately record the open-ocean contemporaneous seawater chemistry and productivity. We show here that it is possible to distinguish between the different types of barite by using Sr and S isotopes along with crystal morphology and size characteristics.

A comparison between excess barium and barite as indicators of carbon export

[1] Since Dymond et al. [1992] proposed the paleoproductivity algorithm based on ‘‘Bio-Ba,’’ which relies on a strong correlation between Ba and organic carbon fluxes in sediment traps, this proxy has been applied in many paleoproductivity studies. Barite, the main carrier of particulate barium in the water column and the phase associated with carbon export, has also been suggested as a reliable paleoproductivity proxy in some locations. We demonstrate that Baexcess (total barium minus the fraction associated with terrigenous material) frequently overestimates Babarite (barium associated with the mineral barite), most likely due to the inclusion of barium from phases other than barite and terrigenous silicates (e.g., carbonate, organic matter, opal, Fe-Mn oxides, and hydroxides). A comparison between overlying oceanic carbon export and carbon export derived from Baexcess shows that the Dymond et al. [1992] algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied. Babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 C and Chlorophyll a measurements of primary production. This relationship varies by ocean basin, but with the application of the appropriate f ratio to 14 C and Chlorophyll a primary production estimates, the plot of Babarite accumulation and carbon export for the equatorial Pacific, Atlantic, and Southern Ocean converges to a global relationship that can be used to reconstruct paleo carbon export. INDEX TERMS: 3022 Marine Geology and Geophysics: Marine sediments—processes and transport; 4267 Oceanography: General: Paleoceanography; 4825 Oceanography: Biological and Chemical: Geochemistry; KEYWORDS: paleoproductivity, barite, export production, excess barium, marine sediments Citation: Eagle, M., A. Paytan, K. R. Arrigo, G. van Dijken, and R. W. Murray, A comparison between excess barium and barite as indicators of carbon export, Paleoceanography, 18(1), 1021, doi:10.1029/2002PA000793, 2003.

Selective phosphorus regeneration of sinking marine particles: evidence from 31P-NMR

Phosphorus (P) regeneration and transformation in the oceanic water column and in marine sediments depends on the chemical nature of the sinking particulate P pool. For the first time, we have characterized the molecular composition of this pool, in various oceanic settings and water depths, using 31 P nuclear magnetic resonance (NMR) spectroscopy. Both inorganic P (orthophosphate, pyrophosphate, and polyphosphate) and organic P compounds (orthophosphate monoesters, orthophosphate diesters, and phosphonates) were identified. The inorganic P is present predominantly as orthophosphate with small amounts (<10%) of pyro- and polyphosphates. These inorganic compounds may be at least partially of biological origin. The relatively high abundance of inorganic P suggests that considerable transformation from the organic to the inorganic pool occurs in the water column. Some of this inorganic P may be present in association with mineral phases (apatite, clays, and oxyhydroxides) and thus may not be bioavailable. The distribution of organic P compounds in the sinking particulate matter pool is generally similar in composition to phytoplankton and significantly different than in the dissolved organic matter (DOM) pool. Results indicate that in most oceanic regions the majority of P regeneration occurs at very shallow depths. However, in the Ross Sea, a significant fraction of organic P is exported to depth below the euphotic zone. Hydrolysis of P compounds continues throughout the water column as indicated by a decrease in total particulate P with depth and a relative decrease in the organic P fraction at some sites. Orthophosphate monoesters dominate the organic P pool at all locations, followed by orthophosphate diesters. Phosphonates are present in a few samples but never contribute more than 6% of total extractable P compared to 25% abundance in the dissolved organic P (DOP) pool. This work shows that considerable spatial and temporal variability in the molecular composition of sinking particulate P exists. A more systematic study is needed to assess the different environmental parameters that affect the composition of particulate P and result in this variability. D 2003 Elsevier Science B.V. All rights reserved.

Benthic Ba fluxes in the central Equatorial Pacific, implications for the oceanic Ba cycle

High resolution pore-water dissolved Ba concentration-depth profiles were determined at seven sites across an Equatorial Pacific productivity gradient from 12°S to 9°N, at 140°W. These data are important for understanding the physical, chemical, and biological controls on Ba recycling in the ocean, and for evaluating the paleo-oceanographic significance of Ba content in central Equatorial Pacific sediments. Pore-water Ba concentrations at all sites are higher than in the overlying bottom water, leading to a diffusive flux of Ba into the ocean. A pronounced subsurface concentration maximum exceeding barite solubility characterizes the dissolved Ba pore-water profiles, suggesting that the Ba regenerated in the upper few millimeters of sediment is not controlled by barite solubility. A few centimeters down-core Ba concentrations reach a relatively constant value of approximately barite saturation. The benthic Ba flux shows a clear zonal trend, with a maximum between 2°S and 2°N, most probably due to higher productivity at the equatorial divergence zone, and with lowest values at the southern and northern extremes of the transect. The dissolved Ba flux between 2°S and 2°N is ∼ 30 nmol cm−2 yr−1 and drops to 6 nmol cm−2 yr−1 at 12°S. Even the lowest fluxes are significantly higher than those previously reported for the open ocean. In the Equatorial Pacific the calculated Ba recycling efficiency is about 70%. Thus, ∼ 30% of the particulate Ba flux to the deep ocean is preserved in the sediments, compared with less than 1% for organic carbon and ∼ 5% for biogenic silica. Mass balance calculation of the oceanic Ba cycle, using a two-box model, implies benthic Ba fluxes similar to those reported here for a steady-state ocean.

Calcium isotope constraints on the end-Permian mass extinction.

The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (δ13C) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (δ44/40Ca) composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction. Here we report δ44/40Ca across the Permian-Triassic boundary from marine limestone in south China. The δ44/40Ca exhibits a transient negative excursion of ∼0.3‰ over a few hundred thousand years or less, which we interpret to reflect a change in the global δ44/40Ca composition of seawater. CO2-driven ocean acidification best explains the coincidence of the δ44/40Ca excursion with negative excursions in the δ13C of carbonates and organic matter and the preferential extinction of heavily calcified marine animals. Calcium isotope constraints on carbon cycle calculations suggest that the average δ13C of CO2 released was heavier than -28‰ and more likely near -15‰; these values indicate a source containing substantial amounts of mantle- or carbonate-derived carbon. Collectively, the results point toward Siberian Trap volcanism as the trigger of mass extinction.

Reduced calcification and lack of acclimatization by coral colonies growing in areas of persistent natural acidification

As the surface ocean equilibrates with rising atmospheric CO2, the pH of surface seawater is decreasing with potentially negative impacts on coral calcification. A critical question is whether corals will be able to adapt or acclimate to these changes in seawater chemistry. We use high precision CT scanning of skeletal cores of Porites astreoides, an important Caribbean reef-building coral, to show that calcification rates decrease significantly along a natural gradient in pH and aragonite saturation (Ωarag). This decrease is accompanied by an increase in skeletal erosion and predation by boring organisms. The degree of sensitivity to reduced Ωarag measured on our field corals is consistent with that exhibited by the same species in laboratory CO2 manipulation experiments. We conclude that the Porites corals at our field site were not able to acclimatize enough to prevent the impacts of local ocean acidification on their skeletal growth and development, despite spending their entire lifespan in low pH, low Ωarag seawater.

Spatial Variability in Nitrification Rates and Ammonia-Oxidizing Microbial Communities in the Agriculturally Impacted Elkhorn Slough Estuary, California

ABSTRACT Ammonia oxidation—the microbial oxidation of ammonia to nitrite and the first step in nitrification—plays a central role in nitrogen cycling in coastal and estuarine systems. Nevertheless, questions remain regarding the connection between this biogeochemical process and the diversity and abundance of the mediating microbial community. In this study, we measured nutrient fluxes and rates of sediment nitrification in conjunction with the diversity and abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing betaproteobacteria (β-AOB). Sediments were examined from four sites in Elkhorn Slough, a small agriculturally impacted coastal California estuary that opens into Monterey Bay. Using an intact sediment core flowthrough incubation system, we observed significant correlations among NO3 −, NO2 −, NH4 +, and PO4 3+ fluxes, indicating a tight coupling of sediment biogeochemical processes. 15N-based measurements of nitrification rates revealed higher rates at the less impacted, lower-nutrient sites than at the more heavily impacted, nutrient-rich sites. Quantitative PCR analyses revealed that β-AOB amoA (encoding ammonia monooxygenase subunit A) gene copies outnumbered AOA amoA gene copies by factors ranging from 2- to 236-fold across the four sites. Sites with high nitrification rates primarily contained marine/estuarine Nitrosospira-like bacterial amoA sequences and phylogenetically diverse archaeal amoA sequences. Sites with low nitrification rates were dominated by estuarine Nitrosomonas-like amoA sequences and archaeal amoA sequences similar to those previously described in soils. This is the first report measuring AOA and β-AOB amoA abundance in conjunction with 15N-based nitrification rates in estuary sediments.

A Dynamic Marine Calcium Cycle During the Past 28 Million Years

Multiple lines of evidence have shown that the isotopic composition and concentration of calcium in seawater have changed over the past 28 million years. A high-resolution, continuous seawater calcium isotope ratio curve from marine (pelagic) barite reveals distinct features in the evolution of the seawater calcium isotopic ratio suggesting changes in seawater calcium concentrations. The most pronounced increase in the δ44/40Ca value of seawater (of 0.3 per mil) occurred over roughly 4 million years following a period of low values around 13 million years ago. The major change in marine calcium corresponds to a climatic transition and global change in the carbon cycle and suggests a reorganization of the global biogeochemical system.