Sue Vink

On the use of dissolved aluminum in surface waters to estimate dust deposition to the ocean

The concentration of dissolved Al in surface waters from various oceanic regimes is used in a simple model to calculate the annual amount of dust deposited to the surface ocean. Calculated values range from 0.015 to 9.9 g dust m−2 yr−1. Comparison of these calculated dust depositions with independent dust deposition estimates obtained from direct measurements, suspended atmospheric dust loads, or sediment traps show remarkably good agreement over approximately 3 orders of magnitude. In regions where the agreement between the model and other estimates is weakest, it is anticipated that local scaling of model parameters such as mixed layer depth and surface water residence time, will lead to improved agreement. Since surface water Al concentrations appear to be driven primarily by dust deposition, the distribution of dissolved Al in surface waters can be used to investigate the systematics of the delivery of other biologically important trace elements, for example, Fe, to the surface of the remote ocean by this route. In addition, temporal variations in surface water Al concentrations can be used to investigate the biogeochemical consequences to the surface ocean of large-scale changes in atmospheric dust loads driven by decadal-scale climatic variations.

Tomales bay metabolism: CNP stoichiometry and ecosystem heterotrophy at the land-sea interface

Bays and estuaries receive inputs from the adjacent land and exchange materials with the coastal ocean. Net system metabolism records the role of such land-sea interface ecosystems in altering the chemical state of essential plant nutrients. Water and salt budgets have been constructed for Tomales Bay, California, in order to estimate water advective and mixing exchange rates between the bay and coastal ocean over 2 years. Net non-conservative fluxes of dissolved P, N and C were calculated. The bay is a net source for dissolved P, C and total alkalinity, and is a net sink for dissolved fixed N. Stoichiometric analysis can be used to interpret the non-conservative nutrient fluxes. The dissolved P source is interpreted to be the result of net oxidation of approximately 10 mmol organic C m−2 day−1. CO2 released by this oxidation largely escapes to the atmosphere. This net respiration is about 12% of the total system respiration. Most dissolved inorganic N liberated during the oxidation is not exported hydrographically; rather, the bay is a net sink of dissolved fixed N. This N is assumed to be lost from the water via denitrification (3·2 mmol m−2 day−1). Sulphate reduction (5·1 mmol m−2 day−1) is also an important component of respiration in this system. Denitrification is a minor component of gross C metabolism, but is the major sink of N in this system. The organic matter driving this net heterotrophy may be of either terrestrial or marine origin.

Dissolved Fe in the upper waters of the Pacific sector of the Southern Ocean

The concentration of dissolved Fe was determined in upper ocean waters along 170 degreesW between 53 and 72 degreesS during four cruises between October 1997 and March 1998 as part of the US-JGOFS Southern Ocean Antarctic Polar Frontal Zone cruises. Fe concentrations were extremely variable in both space and time as a result of advection of meso-scale eddys through the region. Observed values ranged from a maximum of 0.34 nM at 64 degreesS in November next to the retreating ice-edge to 0.075 nM in March at 71 degreesS in the northern Ross Sea gyre. In general, the highest average mixed-layer Fe concentrations and the largest seasonal changes were observed in the two frontal zones at similar to 60 degreesS and similar to 64 degreesS. Formation of deep mixed layers during winter and the entrainment of sub-surface waters enriched in Fe is the primary source of this element to surface waters in this region of the Southern Ocean. Additionally, upwelling of circumpolar deep water in the circumpolar current along its northern boundary at the Polar Front and its southern boundary at the Southern Antarctic Circumpolar Current Front is an important mechanism supplying Fe to surface waters in these areas throughout the summer. Comparison of integrated Fe concentrations and Th-derived POC export and N drawdown all suggest that the maximum changes in these properties are comparable to those that would be predicted by Fe availability. Fe concentrations determined by shipboard Flow Injection Analysis (Measures et al., Mar. Chem. 50 (1995) 3) were significantly higher than those found in replicate samples determined by shored based flameless atomic absorption spectrophotometry after preconcentration by chelation-solvent extraction (Johnson et al., Mar. Chem. 57 (1997) 137). The concentration differences, which appear to be restricted to the upper 200-300 m, do not appear to arise from different sampling or handling processes but instead are believed to result from the different sensitivity of the methods to organic fractions of Fe in seawater

Environmental health impacts of unconventional natural gas development: A review of the current strength of evidence

Rapid global expansion of unconventional natural gas development (UNGD) raises environmental health concerns. Many studies present information on these concerns, yet the strength of epidemiological evidence remains tenuous. This paper is a review of the strength of evidence in scientific reporting of environmental hazards from UNGD activities associated with adverse human health outcomes. Studies were drawn from peer-reviewed and grey literature following a systematic search. Five databases were searched for studies published from January 1995 through March 2014 using key search terms relevant to environmental health. Studies were screened, ranked and then reviewed according to the strength of the evidence presented on adverse environmental health outcomes associated with UNGD. The initial searches yielded >1000 studies, but this was reduced to 109 relevant studies after the ranking process. Only seven studies were considered highly relevant based on strength of evidence. Articles spanned several relevant topics, but most focussed on impacts on typical environmental media, such as water and air, with much of the health impacts inferred rather than evidenced. Additionally, the majority of studies focussed on short-term, rather than long-term, health impacts, which is expected considering the timeframe of UNGD; therefore, very few studies examined health outcomes with longer latencies such as cancer or developmental outcomes. Current scientific evidence for UNGD that demonstrates associations between adverse health outcomes directly with environmental health hazards resulting from UNGD activities generally lacks methodological rigour. Importantly, however, there is also no evidence to rule out such health impacts. While the current evidence in the scientific research reporting leaves questions unanswered about the actual environmental health impacts, public health concerns remain intense. This is a clear gap in the scientific knowledge that requires urgent attention.

Primary productivity and its regulation in the Pacific Sector of the Southern Ocean

We measured primary productivity in the Pacific Sector of the Southern Ocean as part of the Joint Global Ocean Flux Study. We collected data along 170degrees W from 54 degreesS to 72 degreesS on four cruises during the austral growing season of 1997-1998. The cruises crossed the Subantarctic Front, the Antarctic Polar Front (APF), the Southern Antarctic Circumpolar Current (ACC) Front, and the Southern Boundary of the ACC. Primary productivity and chlorophyll a increased rapidly in spring, peaked in summer, and decreased rapidly in fall, following the seasonal pattern of irradiance. In early spring (October), primary productivity was 20 mmol C m(-2) d(-1) and increased to 54 mmol C m(-2) d(-1) within 3 weeks. During peak irradiance (December), productivity reached its maximum throughout the study area with values ranging from 33 to 93 mmol C m(-2) d(-1) depending on station location. By February, average productivity dropped to 20+/-1 mmol C m(-2) d(-1), and individual station values reached a minimum of 13 mmol C m(-2) d(-1). In early spring, chlorophyll was less than 0.5 mg Chl m(-3) throughout the study area. In late spring and early summer, chlorophyll values were between 0.15 and 1.5 mg Chl m(-3) depending on station location. By late summer, chlorophyll decreased to less than 0.3 mg Chl m(-3) across the study region. Highest absolute values of productivity and biomass occurred near the southward-propagating Si gradient (DeltaSi(max)). A spatial gradient in photosynthetic performance correlated with DeltaSi(max): photosynthetic performance was elevated in low silicic acid waters (less than 10 muM) to the north of DeltaSi(max) and was depressed in high silicic acid waters (greater than 30 muM) to the south of DeltaSi(max) Photosynthetic performance also was correlated with iron-enrichment response: when photosynthetic performance was low, iron-enrichment response was high, and when photosynthetic performance was high, iron-enrichment response was low. These results suggest that phytoplankton were iron sufficient north of DeltaSi(max) and iron limited south of DeltaSi(max). We argue that the southward-traveling DeltaSi(max), the APF, and the location of upwelling, iron-rich Upper Circumpolar Deep Water (UCDW) define three regions with differing iron sufficiency. Furthermore, we suggest that a winter recharge of upwelled, iron-rich UCDW within the Antarctic and Southern ACC Zones provides enough iron to support a diatom bloom that annually propagates poleward across the Antarctic and Southern ACC Zones to the Southern Boundary of the ACC, where the absence of UCDW prevents the blooms progression into the Subpolar Regime

Distribution of phosphorus in sediments from Tomales Bay, California

Abstract The distribution of phosphorus among six sequentially extracted fractions was determined in suspended load and bottom sediments from Lagunitas Creek and Tomales Bay, California. The sequential extraction scheme was a modification of the sedex scheme of Ruttenberg (1992), using the surfactant sodium dodecyl sulfate (SDS) to extract organic phosphorus. SDS effectively removed organic phosphorus from sediments with little interference from inorganic phosphorus containing phases. The distribution of phosphorus in the sequentially extracted fractions was similar in suspended load and bottom sediments collected from Lagunitas Creek and the bay. The concentration of phosphorus in CDB-extractable iron oxide phases was below detection in all samples. Most of the phosphorus (70–80%) contained in these sediments was found in the organic and residual phases. Porewaters from sediment cores were analyzed for dissolved inorganic carbon, ammonium, phosphate, sulfate, iron, calcium and fluoride. Within bay sediments, porewaters were depleted in phosphate relative to dissolved inorganic carbon and ammonium, suggesting that phosphate released from organic matter decomposition is being removed from the porewaters. Sequential extraction results suggest that approximately 15% of the phosphate released from organic matter decomposition could be removed from the porewaters by adsorption into the exchangeable phosphorus fraction and an additional 3% may be precipitated as authigenic phosphate minerals. The remaining phosphate (82%) released from organic matter decomposition must be either taken up within the sediment mixed layer (0–40 cm) or escapes to the overlying water column.

Importance of terrestrially-derived, particulate phosphorus to phosphorus dynamics in a west coast estuary

Allochthonous inputs of suspended particulate matter from freshwater environments to estuaries influence nutrient cycling and ecosystem metabolism. Contributions of different biogeochemical reactions to phosphorus dynamics in Tomales Bay, California, were determined by measuring dissolved inorganic phosphorus exchange between water and suspended particulate matter in response to changes in salinity, pH, and sediment redox. In serum bottle incubations of suspended particulate matter collected from the major tributary to the bay, dissolved inorganic phosphorus release increased with salinity during the initial 8 h; between 1–3 d, however, rates of release were similar among treatments of 0 psu, 16 psu, 24 psu, and 32 psu. Release was variable over the pH range 4–8.5, but dissolved inorganic phosphorus releases from sediments incubated for 24 h at the pH of fresh water (7.3) and seawater (8.1) were similarly small. Under oxidizing conditions, dissolved inorganic phosphorus release was small or dissolved inorganic phosphorus was taken up by particulate matter with total P content <50 μmoles P g−1; release was greater from suspended particulate matter with total phosphorus content >50 μmoles P g−1. In contrast, under reducing conditions maintained by addition of free sulfide (HS−), dissolved inorganic phosphorus was released from particles at all concentrations of total phosphorus in suspended particulate matter, presumably from the reduction of iron oxides. Since extrapolated dissolved inorganic phosphorus release from this abiotic source can account for only 12.5% of the total dissolved inorganic phosphorus flux from Tomales Bay sediments, we conclude most release from particles is due to organic matter oxidation that occurs after estuarine deposition. The abiotic, sedimentary flux of dissolved inorganic phosphorus, however, could contribute up to 30% of the observed net export of dissolved inorganic phosphorus from the entire estuary.

Quantifying ecosystem metabolism in the middle reaches of Murrumbidgee River during irrigation flow releases

The relative importance of floodplain carbon inputs and in-stream metabolic processes have not been well quantified in major Australian rivers. We quantified seasonal phytoplankton primary production and net ecosystem production during irrigation flow regimes at four sites each located ∼100 km apart in the middle Murrumbidgee River. During flow periods dominated by storage release, ecosystem gross primary productivity, system respiration and phytoplankton chlorophyll concentrations all increased downstream so that overall net ecosystem metabolism was strongly net heterotrophic upstream and closer to balanced downstream. Phytoplankton production dominated ecosystem production throughout the entire reach and was likely to have been phosphorus limited throughout the study. Additionally, phytoplankton biomass was limited by short residence times at the upstream sites and nitrogen limited downstream in summer, despite an increase in turbidity. Both production and respiration rates were generally lower in winter, as expected, owing to lower temperatures.

Phytoplankton pigment distribution in relation to silicic acid, iron and the physical structure across the Antarctic Polar Front, 170°W, during austral summer

In order to study the factors controlling the phytoplankton distribution across the Antarctic Polar Frontal Region (PFR), surface pigment samples were collected during austral summer (January/February 1998) near 170°W. Both the Polar Front (PF) and the Southern Antarctic Circumpolar Current Front (SACCF) were regions of enhanced accumulation of phytoplankton pigments. The mesoscale survey across the PF revealed two distinct phytoplankton assemblages on either side of the front. The phytoplankton community was dominated by diatoms south of the PF and by nanoflagellates (primarily by prymnesiophytes) to the north. Surprisingly, chlorophyll a concentrations did not correlate with mixed-layer depths. However, an increase of the dominance of diatoms over prymnesiophytes was observed with decreasing mixed-layer depths. Despite this relationship, we conclude that the average light availability in the mixed layer was not an important factor influencing the shift in phytoplankton composition across the PF. Although no correlation was found between the surface distribution of the major phytoplankton taxa and dissolved iron or silicic acid concentrations, the location of the strongest vertical gradient in silicic acid and iron concentration coincides with the maximum abundance of diatoms. We conclude that the difference in taxonomic composition is a result of increased silicic acid and iron flux to the upper mixed layer as a result of the increased vertical gradient of these key nutrients south of the front.

Sulfate reduction and sediment metabolism in Tomales Bay, California

Sulfate reduction rates (SRR) in subtidal sediments of Tomales Bay, California, were variable by sediment type, season and depth. Higher rates were measured in near-surface muds during summer (up to 45 nmol cm-3 h-1), with lower rates in sandy sediments, in winter and deeper in the sediment. Calculations of annual, average SRR throughout the upper 20 cm of muddy subtidal sediments (about 30 mmol S m-2 d-1) were much larger than previously reported net estimates of SRR derived from both benthic alkalinity flux measurements and bay wide, budget stoichiometry (3.5 and 2.6 mmol m-2 d-1, respectively), indicating that most reduced sulfur in these upper, well-mixed sediments is re-oxidized. A portion of the net alkalinity flux across the sediment surface may be derived from sulfate reduction in deeper sediments, estimated from sulfate depletion profiles at 1.5 mmol m-2 d-1. A small net flux of CO2 measured in benthic chambers despite a large SRR suggests that sediment sinks for CO2 must also exist (e.g., benthic microalgae).