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Wan Z.,Danish Meteorological Institute | Jonasson L.,Danish Meteorological Institute | Bi H.,Chesapeake Biological Laboratory
Ocean Science | Year: 2011

The N/P ratio of nutrient uptake, the change of dissolved inorganic nitrogen (DIN) relative to the change of dissolved inorganic phosphorus (DIP), is a key parameter for many ecological models. In the Baltic Sea ecosystem, the N/P ratio of nutrient uptake varies among different basins and different seasons. The N/P ratio of nutrient alteration, i.e., the ratio of DIN to DIP altered before and after spring blooms, is not the same as the N/P ratio of nutrient uptake, but the former can be regarded as an indicator of the latter in the Baltic Sea. Based on the observed N/P ratio of nutrient alteration, we hypothesize a non-Redfield N/P ratio of nutrient uptake. The 3-D-ecosystem model ERGOM coupled with the circulation model DMI-BSHcmod was used to test this hypothesis. When the Redfield ratio was used in the model, the DIP surplus after spring blooms was too high and resulted in excessive growth of cyanobacteria and too much nitrogen fixation. When the non-Redfield ratio was used in the model, these problems tended to disappear. In summary, we show that: (1) the Redfield N/P ratio of nutrient uptake in the Baltic Sea tends to be too high; (2) a N/P ratio of 10:1 appears to work better than the Redfield value; and (3) the N/P ratio of nutrient uptake in the Baltic Proper during spring blooms is around 6:1. As the model limitation using one identical value for two N/P ratios for nutrient uptake and remineralization, the quantitative conclusions are only convincing as a model parameter even though it obviously improves model predictions. Whether this model parameter is consistent with the biological nutrient uptake is worth being further verified with some laboratory investigations or simulations using a more sophisticated model with independent N/P ratios for nutrient uptake and remineralization. © Author(s) 2011.

Wan Z.,Danish Meteorological Institute | Bi H.,Chesapeake Biological Laboratory
Ecological Modelling | Year: 2014

Observation data on surface dissolved inorganic nutrients in 2000-2009 at 15 stations in the Baltic Sea were used to analyze the ratio of nitrogen change to phosphorus change (N/P) before and after spring blooms. The ratios of nutrient N/P before and after spring blooms vary from 6.6:1 to 41.5:1. To estimate the spatially varied plankton N/P ratios, the observed nutrient N/P ratios as proxies for plankton N/P ratios are used to extrapolate a spatial pattern, and then the spatial pattern is adjusted by comparing observations and model results and the best fit spatial pattern is selected to discern the horizontal variability of plankton N/P, i.e., low in the center of the Baltic, relatively high away from the center. To examine the potential impact of spatially varied N/P ratios on phytoplankton and nutrients, a three dimensional physical-biogeochemical coupled model is used to compare two scenarios: spatially varied plankton N/P ratios versus a constant N/P ratio. When comparing model results to observation data, model results with spatially varied N/P ratios showed consistent improvements over model results with a constant N/P ratio, specifically in dissolved inorganic nitrogen, dissolved inorganic phosphorus, chlorophyll. Therefore, we concluded that the spatially varied N/P ratios can feature the horizontal distribution of plankton N/P in the Baltic Sea. Furthermore, the impacts of the variable plankton N/P ratio on primary production and nitrogen fixation are also investigated using the 3D ecosystem model. The estimated primary production and nitrogen fixation using the constant N/P ratio of 16:1 are 38% and 317% higher, respectively, than those estimates using the variable N/P ratio. © 2013 Elsevier B.V.

Barry J.P.,Monterey Bay Aquarium Research Institute | Buck K.R.,Monterey Bay Aquarium Research Institute | Lovera C.,Monterey Bay Aquarium Research Institute | Brewer P.G.,Monterey Bay Aquarium Research Institute | And 9 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2013

The effects of low-pH, high-pCO2 conditions on deep-sea organisms were examined during four deep-sea CO2 release experiments simulating deep-ocean C sequestration by the direct injection of CO2 into the deep sea. We examined the survival of common deep-sea, benthic organisms (microbes; macrofauna, dominated by Polychaeta, Nematoda, Crustacea, Mollusca; megafauna, Echinodermata, Mollusca, Pisces) exposed to low-pH waters emanating as a dissolution plume from pools of liquid carbon dioxide released on the seabed during four abyssal CO2-release experiments. Microbial abundance in deep-sea sediments was unchanged in one experiment, but increased under environmental hypercapnia during another, where the microbial assemblage may have benefited indirectly from the negative impact of low-pH conditions on other taxa. Lower abyssal metazoans exhibited low survival rates near CO2 pools. No urchins or holothurians survived during 30-42 days of exposure to episodic, but severe environmental hypercapnia during one experiment (E1; pH reduced by as much as ca. 1.4 units). These large pH reductions also caused 75% mortality for the deep-sea amphipod, Haploops lodo, near CO2 pools. Survival under smaller pH reductions (δpH<0.4 units) in other experiments (E2, E3, E5) was higher for all taxa, including echinoderms. Gastropods, cephalopods, and fish were more tolerant than most other taxa. The gastropod Retimohnia sp. and octopus Benthoctopus sp. survived exposure to pH reductions that episodically reached -0.3pH units. Ninety percent of abyssal zoarcids (Pachycara bulbiceps) survived exposure to pH changes reaching ca. -0.3pH units during 30-42 day-long experiments. © 2013 Elsevier Ltd.

Underwood S.,University of North Carolina at Chapel Hill | Lapham L.,Chesapeake Biological Laboratory | Teske A.,University of North Carolina at Chapel Hill | Lloyd K.G.,University of North Carolina at Chapel Hill
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2015

The Deepwater Horizon disaster caused a shift in microbial communities in Gulf of Mexico seawater, but less is known about the baseline for microbial communities in the underlying sediments. We compared 16S rRNA and functional gene sequences deriving from DNA and RNA with geochemical profiles (sulfate and methane concentrations, δ13C of methane and carbon dioxide, and chloride concentrations) of a sediment gravity core from the upper continental slope of the northwestern Gulf of Mexico (MC118) in 2008, 15km from the spill site. The highest number of archaeal sequences were ANME-1 and ANME-2 archaea in the sulfate-reducing upper core segments (12 and 42cmbsf), ANME-1 and Methanomicrobiales in the middle methanogenic depths (200 and 235cmbsf), and ANME-1 at the deepest depths (309, 400, and 424cmbsf). The presence of mcrA gene transcripts showed that members of the ANME-1 group are active throughout the core and transcribe the mcrA gene, a key gene of methanogenesis and anaerobic methane oxidation. The bacterial community consists mostly of members of the Deltaproteobacteria, Chloroflexi, Cytophaga, Epsilonproteobacteria, and the Japan Sea Group 1 throughout the core. The commonly detected genera of gammaproteobacterial hydrocarbon-degrading bacteria in the water column are not found in this sediment survey, indicating that the benthic sediment is an unlikely reservoir for these aerobes. However, the sediments contain members of the sulfate-reducing families Desulfobulbaceae and Desulfobacteraceae, some members of which degrade and completely oxidize aromatic hydrocarbons and alkanes, and the Desulfobacterium anilini lineage of obligately aromatics-degrading sulfate reducers. Thus, the benthic sediments are the most likely reservoir for the active deltaproteobacterial populations that were observed repeatedly after the Deepwater Horizon spill in the fall of 2010. © 2015 Elsevier Ltd.

Shillinger G.L.,Stanford University | Shillinger G.L.,Center for Ocean Solutions | Swithenbank A.M.,Stanford University | Bailey H.,National Oceanic and Atmospheric Administration | And 9 more authors.
Marine Ecology Progress Series | Year: 2011

Leatherback turtles are the largest and widest ranging turtle species, and spend much of their time in the offshore pelagic environment. However, the high seas have thus far received little management attention to protect their ecosystems and biodiversity. We tagged 46 female leatherback turtles with satellite transmitters at Playa Grande, Costa Rica from 2004 to 2007. In the present study, we analyzed the vertical and horizontal habitat preferences of these leatherback turtles in the South Pacific Ocean. The turtles exhibited short, shallow dives during their migration southward (mean depth: 45 m; mean duration: 23.6 min), followed by deeper, longer dives (mean depth: 56.7 m; mean duration: 26.4 min) in the South Pacific Gyre that probably indicated searching for prey. We integrated the horizontal movements with remotely sensed oceanographic data to determine the turtles' response to the environment, and applied this information to recommendations for conservation in the pelagic environment. A generalized additive mixed model applied to the daily turtle travel rates confirmed that slower travel rates occurred at cooler sea surface temperatures, higher chlorophyll a concentration and stronger vertical Ekman upwelling, all of which are considered favorable foraging conditions. The southern terminus (35 to 37° S) of the leatherback tracks was also in an area of increased mesoscale activity that might act as a physical mechanism to aggregate their prey, gelatinous zooplankton. However, this could also act as a thermal limit to their distribution. This characterization of leatherback habitat use could aid the development of management efforts within the South Pacific Ocean to reduce mortality of leatherback turtles from fisheries interactions. © Inter-Research 2011.

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