Alkalinity and pH in the Southern Chesapeake Bay and the James River Estuary

The ranges of alkalinity and pH in the southern Chesapeake Bay and the James River estuary were 2.25 meq·liter−1 at 32‰ to \u3c0.85 at salinities below 6‰ and 7.5– 8.3 during the sampling period. Alkalinity is linearly related to salinity in southern Chesapeake Bay. In the James River estuary, the relationship is more complicated as a result of the mixing of various sources of water or the removal of alkalinity. pH values increase with salinity. The variations in pH may be caused by the salinity‐dependence of the apparent dissociation constants of carbonic acid. © 1979, by the Association for the Sciences of Limnology and Oceanography, Inc

Dissolved inorganic and particulate iodine in the oceans

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts institute of Technology and the Woods Hole Oceanographic Institution February 1976Analytical methods have been developed for the determination of iodate, iodide and particulate iodine in sea water. Iodate is converted to tri-iodide and the absorbance of tri-iodide at 353 nm is measured. The precision of this method is ca. ±3%. Iodide is first separated from most other anions by an AG 1-x8 anion exchange column and then precipitated as palladous iodide with elemental palladium as the carrier. The precipitate is analyzed by neutron activation analysis. The precision of the method is ±5% and the reagent blank is 0.005 uM. Marine suspended matter is collected by passing sea water under pressure through a 0.6 u (37 mm diameter) Nuclepore filter. The iodine content of the particles is determined by neutron activation analysis. The method has excellent reproducibility and the filter blank is ca. 3 ng. Iodate is depleted in the surface waters of the Equatorial Atlantic. The depletion is more pronounced than in the Argentine Basin and possibly reflects the higher productivity in the equatorial area. Superimposed on this feature, a thin lens of water, of a few tens of meters thick and with high iodate concentrations, can be traced across the Atlantic. Along the equator, this lens occurs at 80 m at 33˚W and rises upwards to 55 m at 10˚W and it coincides with a core of highly saline water which is characteristic of the Equatorial Undercurrent. Longitudinal sections reflect the complexity of the equatorial current system. At least three cores of water with high iodate concentrations may be identified. These waters may be transported to the equatorial region from the highly productive areas along the north-western and western African coasts and the Amazon plume. In anoxic basins, the concentration of iodide increases rapidly in the mixing zone from 0.02 uM to 0.44 uM in the Cariaco Trench and from 0.01 uM to 0.23 uM in the Black Sea. The iodate concentration, meanwhile. decreases to zero. A maximum in the total iodine to salinity ratio is observed just above the oxygen-sulfide interface (15 to 17 nmoles/g); it is suggestive of particle dissolution in a strong pycnocline. Below the interface, the total iodine to salinity ratio is constant at 12.3 nmoles/g in the anoxic zone of the Cariaco Trench, whereas, in the Black Sea, it increases with depth from 10.0 to 19.4 nmoles/g and suggests a possible flux of iodide from the sediments. By considering the distribution of iodate and iodide in oxic and anoxic basins and our present analytical capability, the lower limit of the pE of the oceans is estimated to be 10.7. Thermodynamic considerations further suggest that the iodide-iodate couple is a poor indica tor for the pE of the oceans with a limited usable range of 10.0 to 10.7. In the Gulf of Maine during the winter of 1974 to 1975. the effect of winter mixing was conspicuous. Uniform concentrations of iodide and iodate were observed in the mixed layer above the sill. The absence of a depletion of iodate and the low iodide concentration (0.04 uM) in the surface waters reflect the low biological activity in this region during winters. Profiles of particulate iodine are characterized by high concentrations in the euphotic zone (>5 ng/kg), and lower concentrations (< 2 ng/kg) at greater depths. Occasionally, high concentrations have also been observed in the nepheloid layer. The iodine-containing particles are probably biogenic. A section in the Western Atlantic from 75°N to 55˚S shows evidence of the transport of particles along isopycnals and the re-suspension of surface sediments to considerable distance from the bottom. The standing crops in the top 200 m may be qualitatively correlated with the primary productivity. Thermodynamic considerations show that iodide is a metastable form at the pH of sea water. Laboratory studies fail to show the oxidation of iodide at measurable rates. Elemental iodine is unstable in sea water and undergoes hydrolysis to form hypoiodous acid in seconds. Hypoiodous acid is also unstable and has a life time of minutes to hours. It may react with organic compounds to form iodinated derivatives or it may be reduced to iodide by a reducing agent. The disproportionation of hypoiodite to form iodate seems to be a slower process. A possible chemical cycle for iodine in the marine environment is proposed.This work was supported at various phases by NSF Grant GA-13574, NSF-IDOE Grant GX 33295, NSF Grant DES 74- 22292 and by a research fellowship from the Woods Hole Oceanographic Institution

The Effect of Spectral Composition on the Photochemical Production of Hydrogen Peroxide in Lake Water

Hydrogen peroxide was produced when samples of lake water were exposed to direct or filtered sunlight in which UV or UV(B+C) light was selectively removed. In all cases, the concentration of hydrogen peroxide increased linearly with time-integrated irradiance. While both visible and UV light can induce the formation of hydrogen peroxide, the contribution from the latter was disproportionately large as it was responsible for about two-thirds of the formation of hydrogen peroxide. Among the UV lights, the contributions from UV-A and UV-(B+C) light were 70% and 30% respectively. The contribution from UV-A light was equivalent to about one half of the total production of hydrogen peroxide. Thus, relative to its contribution to the total irradiance in the solar spectrum, UV-A light is the most efficient type of light for the formation of hydrogen peroxide in lake waters

Upper Water Structure and Mixed Layer Depth in Tropical Waters: The SEATS Station in the Northern South China Sea

The variability of the upper water hydrographic structure, the efficacy of the different schemes for estimating the mixed layer depth (MLD), the inter-comparability estimation of the MLDs and diurnal and intra-annual MLD climatology in the tropical waters in the northern South China Sea were accessed in 702 depth-profiles of potential temperature (θ) and salinity collected in 64 cruises between 17.5 and 18.5°N and 115.3 and 116.3°E from 1997 to 2013. The hydrographic structure may be subdivided into three principal types: the classical type, with quasi-isopycnal surface mixed layer followed by an abrupt increase in the depth-gradient in θ and potential density (σθ) to mark the MLD; the stepwise type, with one or more small stepwise decreases in θ and/or increases in σθ in the mixed layer; and the graded type, with a general decrease in θ and increases in σθ with depth into the main pycnocline without a clear break to mark the MLD. These three types of upper waters were found in 75, 10, and 15% of the cruises. Out. of the 10 schemes for estimating the MLD, only the fixed temperature difference method of 0.5 and 0.8°C from the 10-m temperature yielded consistent results, with root mean square error and mean absolute percentage difference of 2 m and 2%. MLD varied diurnally with an average standard deviation of 4 m from the mean. The monthly average MLD reached a maximum of 80 m in December/January and dropped to a minimum of 25 m in May

The Transformation of Iodate to Iodide in Marine Phytoplankton Cultures

Six species of phytoplankton, representing 6 major phylogenetic groups (2 oceanic species: a cyanobacteria, Synechococcus sp., and a coccolithophorid, Emiliania huxleyi; and 4 coastal species: a prasinophyte, Tetraselmis sp., the green algae Dunaliella tertiolecta, the diatom Skeletonema costatum and a dinoflagellate Amphidinium carterae) were tested for their ability to reduce iodate to iodide in batch cultures. They all did so to varying degrees. Thus, the reduction of iodate to iodide by phytoplankton may be a general phenomenon in the marine environment. At ambient concentrations of iodate, the rates of depletion of iodate and appearance of iodide varied between 0.8 and 0.02, and between 0.3 and 0.02 nmol µg chlorophyll a–1 d–1, respectively. E. huxleyi was the least efficient while A. carterae was the most efficient in the depletion of iodate. However, in the formation of iodide, while E. huxleyi was also the least efficient, Synechococcus sp. were the most efficient. The rates of appearance of iodide were noticeably slower than the corresponding rates of depletion of iodate, suggesting that part of the iodate might have been converted to forms of iodine other than iodide in these cases. The slight mismatch in the rank order of the rates of depletion of iodate and appearance of iodide between the phytoplankton species was traced to this variable and incomplete conversion of iodate to iodide. These rates were increased by up to over an order of magnitude upon enriching the culture medium with 5 and 10 µM of iodate. The depletion of iodate and appearance of iodide occurred in all growth phases. However, the rates might vary with growth phase and the patterns of these variations might be species-specific. Phytoplankton growth was not impeded even under unnaturally high concentrations of iodate implying that there is little interaction between iodine processing and the metabolic activity of cell growth

Climate modulates internal wave activity in the Northern South China Sea

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 831–838, doi:10.1002/2014GL062522.Internal waves (IWs) generated in the Luzon Strait propagate into the Northern South China Sea (NSCS), enhancing biological productivity and affecting coral reefs by modulating nutrient concentrations and temperature. Here we use a state-of-the-art ocean data assimilation system to reconstruct water column stratification in the Luzon Strait as a proxy for IW activity in the NSCS and diagnose mechanisms for its variability. Interannual variability of stratification is driven by intrusions of the Kuroshio Current into the Luzon Strait and freshwater fluxes associated with the El Niño–Southern Oscillation. Warming in the upper 100 m of the ocean caused a trend of increasing IW activity since 1900, consistent with global climate model experiments that show stratification in the Luzon Strait increases in response to radiative forcing. IW activity is expected to increase in the NSCS through the 21st century, with implications for mitigating climate change impacts on coastal ecosystems.This work was supported by NSF award 1220529 to Anne Cohen, by the Academia Sinica (Taiwan) through a thematic project grant to G.T.F.W. and Anne Cohen, by the Alfred P. Sloan Foundation and the WHOI Oceans and Climate Change Institute/Moltz Fellowship through awards to K.B.K., and by an NSF Graduate Research Fellowship to T.M.D.2015-08-1

Mass coral mortality under local amplification of 2°C ocean warming

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 44586, doi:10.1038/srep44586.A 2°C increase in global temperature above pre-industrial levels is considered a reasonable target for avoiding the most devastating impacts of anthropogenic climate change. In June 2015, sea surface temperature (SST) of the South China Sea (SCS) increased by 2 °C in response to the developing Pacific El Niño. On its own, this moderate, short-lived warming was unlikely to cause widespread damage to coral reefs in the region, and the coral reef “Bleaching Alert” alarm was not raised. However, on Dongsha Atoll, in the northern SCS, unusually weak winds created low-flow conditions that amplified the 2°C basin-scale anomaly. Water temperatures on the reef flat, normally indistinguishable from open-ocean SST, exceeded 6°C above normal summertime levels. Mass coral bleaching quickly ensued, killing 40% of the resident coral community in an event unprecedented in at least the past 40 years. Our findings highlight the risks of 2°C ocean warming to coral reef ecosystems when global and local processes align to drive intense heating, with devastating consequences.This research was funded by the National Science Foundation (OCE-1031971 and OCE-1605365 to A.L.C), the Sustainability Science Research Program of the Academia Sinica (G.T.F.W. and A.L.C), a Woods Hole Oceanographic Institution Coastal Ocean Institute award to T.M.D., and a National Science Foundation Graduate Research Fellowship awarded to T.M.D

Validation of the remotely sensed nighttime sea surface temperature in the shallow waters at the Dongsha Atoll

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Terrestrial, Atmospheric and Oceanic Sciences 28 (2017): 517-524, doi:10.3319/TAO.2017.03.30.01.Fine scale temperature structures, which are commonly found in the top few meters of shallow water columns, may result in deviations of the remotely sensed night-time sea surface temperatures (SST) by the MODIS-Aqua sensor (SSTsat) from the bulk sea surface temperatures (SSTbulk) that they purport to represent. The discrepancies between SSTsat and SSTbulk recorded by temperature loggers at eight stations with bottom depths of 2 - 20 m around the Dongsha Atoll (DSA) between June 2013 and May 2015 were examined. The SSTsat had an average cool bias error of -0.43 ± 0.59°C. The bias error was larger in the warmer (> 26°C) waters which were presumably more strongly stratified. The root mean square error (RMSE) between SSTsat and SSTbulk, ±0.73°C, was 25% larger than that reported in the open northern South China Sea. An operational calibration algorithm was developed to increase the accuracy in the estimation of SSTbulk from SSTsat. In addition to removing the cool bias error, this algorithm also reduced the RMSE to virtually the same level as that found in the open northern South China Sea. With the application of the algorithm, in June 2015, the average SST in the lagoon of the DSA was raised by about 0.5°C to 31.1 ± 0.4°C, and the area of lagoon with SSTbulk above 31°C, the median value of the physiological temperature threshold of reef organisms, was increased by 69% to about three quarters of the lagoon.This work was supported in part by the Key Research and Development Program of Shandong Province (grant no. 2015GSF117017) and Ocean University of China (grant no. 201513037 and 201512011) to Pan, and the Academia Sinica through grant titled “Ocean Acidification: Comparative biogeochemistry in shallow-water tropical coral reef ecosystems in a naturally acidic marine environment” to Wong

The Effects of Light and Nitrate Levels on the Relationship Between Nitrate Reductase Activity and (NO3-)-N-15 Uptake: Field Observations in the East China Sea

Nitrate reductase activity (NRA) and 15NO3- uptake (NU) were determined in the East China Sea and the adjoining Kuroshio in May 1996, at six stations covering a range of hydrographic conditions: the nutrient-rich and fresher plume of Changjiang Diluted Water along the Chinese coast, the nutrient-rich upwelling Kuroshio Subsurface Water at the shelf edge northeast of Taiwan, the oligotrophic Kuroshio Surface Water and the mixing zones among these water masses on the shelf. The values of NRA in the surface mixed layer ranged between 16 and 0.1 nM-N h-1, whereas those of NU ranged between 37 and 1 nM-N h-1. Higher NRA and NU were found in the frontal zone between the coastal and shelf waters and in the upwelling zone, whereas the lowest values were found in the surface Kuroshio. The NRA/Chl a ratio increased linearly with increasing NU/primary production ratio in the sequence: Kuroshio \u3c coastal plume \u3c upwelling zone and mixing zones in the shelf. This is probably a reflection of the varying nutrient condition and the relative importance of NU in sustaining the biomass in these regions. In nitrate- and light-replete waters, the average NU/NRA was 1.0 +/- 0.3. NRA was linearly related to NU so that NU = 1.08 (+/- 0.07)NRA (r(2) = 0.79). Thus, NRA may be used for estimating NU in these waters. In nitrate deficient and light-replete waters, the average NU/NRA was 4 +/- 4. These high and variable values of NU/NRA might have been caused by an over-estimation of NU as a result of the stimulatory effect of the added 15NO3-N on phytoplankton growth. Thus, NRA may be a more reliable indicator of the rate of NO3- uptake in oligotrophic waters. In nitrate-replete and light-deficient waters, NU did not correlate well with NRA. The average NU/NRA was 0.7 +/- 0.7. These low and variable values of NU/NRA suggest a possible decoupling between NRA and NU. By using the relationship between NU and NRA in nitrate- and light-replete waters and the depth-integrated inventory of NRA in the photic zone at each station, NU in oligotrophic waters, the coastal plume, upwelling waters and shelf waters can be estimated to be 0.45, 1.55, 3.12, and 3.59 mg-N m-2 h-1 respectively. These values fall well within the range of previously reported values in similar types of water

A Unique Seasonal Pattern in Phytoplankton Biomass in Low-Latitude Waters in the South China Sea

A distinctive seasonal pattern in phytoplankton biomass was observed at the South East Asian Time series Study (SEATS) station (18°N, 116°E) in the northern South China Sea (SCS). Surface chlorophyll-a, depth integrated chlorophyll-a and primary production were elevated to 0.3 mg/m3, ~35 mg/m2 and 300 mg-C/m2/d, respectively, in the winter but stayed low, at 0.1 mg/m3, ~15 mg/m2 and 110 mg-C/m2/d as commonly found in other low latitude waters, in the rest of the year. Concomitantly, soluble reactive phosphate and nitrate+nitrite in the mixed layer also became readily detectable in the winter. The elevation of phytoplankton biomass coincided approximately with the lowest sea surface temperature and the highest wind speed in the year. Only the combined effect of convective overturn by surface cooling and wind-induced mixing could have enhanced vertical mixing sufficiently to make the nutrients in the upper nutricline available for photosynthetic activities and accounted for the higher biomass in the winter