Dr. Matthew C Schwartz

Foraminifera are an important component of benthic communities in oxygen-depleted settings, where they potentially play a significant role in the processing of organic matter. We tracked the uptake of a C-13-labelled algal food source into individual fatty acids in the benthic foraminiferal species Uvigerina ex. gr. semiornata from the Arabian Sea oxygen minimum zone (OMZ). The tracer experiments were conducted on the Pakistan margin during the late/post monsoon period (August-October 2003). A monoculture of the diatom Thalassiosira weisflogii was C-13-labelled and used to simulate a pulse of phytoplankton in two complementary experiments. A lander system was used for in situ incubations at 140m water depth and for 2.5 days in duration. Shipboard laboratory incubations of cores collected at 140 m incorporated an oxystat system to maintain ambient dissolved oxygen concentrations and were terminated after 5 days. Uptake of diatoms was rapid, with a high incorporation of diatom fatty acids into foraminifera after similar to 2 days in both experiments. Ingestion of the diatom food source was indicated by the increase over time in the quantity of diatom biomarker fatty acids in the foraminifera and by the high percentage of C-13 in many of the fatty acids present at the endpoint of both in situ and laboratory-based experiments. These results indicate that U. ex. gr. semiornata rapidly ingested the diatom food source and that these foraminifera will play an important role in the short-term cycling of organic matter within this OMZ environment. The presence of 18:1(n-7) in the experimental foraminifera suggested that U. ex. gr. semiornata also consumed non-labelled bacterial food items. In addition, levels of 20:4(n-6), a PUFA only present in low amounts in the diatom food, increased dramatically in the foraminifera during both the in situ and shipboard experiments, possibly because it was synthesised de novo. This "essential fatty acid" is often abundant in benthic fauna, yet its origins and function have remained unclear. If U. ex. gr. semiornata is capable of de novo synthesis of 20:4(n-6), then it represents a potentially major source of this dietary nutrient in benthic food webs.

The Delaware River and Bay Estuary is one of the major urbanized estuaries of the world. The 100-km long tidal river portion of the estuary suffered from major summer hypoxia in the past due to municipal and industrial inputs in the urban region; the estuary has seen remarkable water quality improvements from recent municipal sewage treatment upgrades. However, the estuary still has extremely high nutrient loading, which appears to not have much adverse impact. Since the biogeochemistry of the estuary has been relatively similar for the past two decades, our multiple year research database is used in this review paper to address broad spatial and seasonal patterns of conditions in the tidal river and 120 km long saline bay. Dissolved oxygen concentrations show impact from allochthonous urban inputs and meteorological forcing as well as biological influences. Nutrient concentrations, although high, do not stimulate excessive algal biomass due to light and multiple nutrient element limitations. Since the bay does not have strong persistent summer stratification, there is little potential for bottom water hypoxia. Elevated chlorophyll concentrations do not exert much influence on light attenuation since resuspended bottom inorganic sediments dominate the turbidity. Dissolved inorganic carbon and dissolved and particulate organic carbon distributions show significant variability from watershed inputs and lesser impact from urban inputs and biological processes. Ratios of dissolved and particulate carbon, nitrogen, and phosphorus help to understand watershed and urban inputs as well as autochthonous biological influences. Owing to the relatively simple geometry of the system and localized anthropogenic inputs as well as a broad spatial and seasonal database, it is possible to develop these biogeochemical trends and correlations for the Delaware Estuary. We suggest that this biogeochemical perspective allows a revised evaluation of estuarine eutrophication that should have generic value for understanding other estuarine and coastal waters.

Porewater concentrations and benthic fluxes of phosphate, silicate, ammonia, nitrate and nitrite were measured at five sites spanning the Pakistan margin oxygen minimum zone (OMZ), in order to characterise the biogeochemical processes occurring, and to assess whether oxygen concentration and a seasonal pulse of organic matter are controlling factors. Typical concentrations of 1-70 mu M, 50-250 mu M, 0-270 mu M, <5 mu M and 0-4 mu M for PO43-, H4SiO4, NH4+, NO3- and NO2-, respectively were obtained. Evidence was found for the occurrence of intense clenitrification, sorption of PO43- onto iron and manganese oxyhydroxides and possibly fluoroapatite precipitation at depth (> 30 cm) in the sediment. These processes are all redox-sensitive, and their intensities varied across the margin, suggesting that oxygen concentration exerts a strong influence over nutrient concentrations and cycling. Variation in nutrient concentrations and fluxes before and after the summer monsoon was limited to an oxygen-driven change to the PO43- profile at one site, indicating that either nutrient profiles do not generally alter on seasonal timescales, or that any impact of the monsoon had subsided before the post-monsoon sampling period. Porewater profile modelling tended to underestimate the magnitude of fluxes, but was in general agreement with the directions of measured fluxes, and in situ and shipboard flux measurements also generally agreed. Phosphate and H4SiO4 concentrations and benthic fluxes on the Pakistan margin were similar to those reported at abyssal sites from around the world, while NH4+ and NOT concentrations and fluxes were comparable to shallower, more productive and/or hypoxic marine settings. (C) 2008 Elsevier Ltd. All rights reserved.

Sedimentary denitrification was measured at sites across the Pakistan Margin oxygen minimum zone (OMZ) during cruises before and after the 2003 Southwest (SW) Monsoon. Denitrification rates were calculated using nitrate fluxes and N-2 production rates in shipboard whole-core incubations and benthic lander deployments, We observed generally good agreement between the sedimentary denitrification rates obtained from nitrate consumption and N-2 production. Results of these investigations indicate that sedimentary denitrification is a persistent process within the Arabian Sea OMZ and the regions proximal to the permanent OMZ (e.g., 140 and 1200 m). Sedimentary denitrification in the region intensified during the SW Monsoon, as noted by the increase in associated rates between the inter-monsoon (April-May 2003) and post-monsoon (September-October 2003) assessments. Sedimentary denitrification was observed at all stations during the inter-monsoon period; nitrate consumption rates ranged from 0.40 to 3.17 mmol N m(-2) d(-1). During the post-monsoon assessment, apparent sedimentary denitrification rates increased in the shallow sites (140 and 300 m), likely in response to a shoaling of the OMZ, but were not definitively observed at the deepest site (1850 m); where observed, post-monsoon sedimentary denitrification rates increased to 0.66-3.78 mmol N m(-2) d(-1). These rates compare favorably to sedimentary denitrification rates obtained in other shelf environments and are higher than abyssal sedimentary denitrification rates. By extrapolating these rates to the entire Pakistan Margin OMZ, we estimate a net annual sedimentary denitrification flux of 1.1-10.5 Tg N yr(-1), moderately higher than current estimates of sedimentary denitrification in this region and in line with estimates of regional sedimentary denitrification in other sites. (C) 2008 Elsevier Ltd. All rights reserved.

Biogeochemical processes and fluxes occurring across the sediment–water interface on continental margins impacted by oxygen minimum zones (OMZs) are important to bioelement cycles, ocean inventories, and productivity. The nature and magnitude of these processes depend heavily on spatial and temporal variability in dissolved O
2 concentrations in bottom waters and porewaters.
In 2003, four research cruises to the Indus margin of the Arabian Sea (Pakistan) were undertaken to survey the benthic biogeochemical processes in the resident OMZ before and after the southwest monsoon. Sediment O
2 microdistribution and consumption rates were measured at five stations along a depth transect (140–1850
m) across the OMZ, during the spring intermonsoon and the late-to-post southwest monsoon periods, using
in situ benthic research platforms (landers). Lander O
2 electrode data show that the intermonsoon and late-to-postmonsoon bottom-water O
2 levels had little to no variation (300
m, no change; 940
m, 1.7–2.8
μM; 1200
m, 10.2–12.6
μM; and 1850
m, 82–80
μM). In contrast, at the shallowest station (140
m), a large fluctuation occurred between the intermonsoon (O
2=44.5
μM) and the late-to-postmonsoon (O
2=1
μM), due to monsoon-forced shoaling of the upper OMZ boundary. Oxygen did not penetrate into the sediments at the 300-m site during either sampling season. During the intermonsoon season at the 140-m site, O
2 penetrated to a depth of ∼3
mm, but no measurable O
2 penetration occurred after the monsoon. At the 940 and 1200-m sites, O
2 penetration into the sediments was small (ca. 1–2
mm at both sites) and did not measurably change between the two sampling seasons. In contrast, at the 1850-m site, O
2 penetration decreased after the monsoon (18–12
mm). Calculated late-to-postmonsoon O
2 consumption rates were generally similar to or lower than intermonsoon values (0 vs. 2.22
mmol
m
−2
d
−1 at 140
m, 0.37 vs. 0.31
mmol
m
−2
d
−1 at 1200
m, and 0.73 vs. 1.01
mmol
m
−2
d
−1 at 1850
m). The relatively small seasonal signal suggests that organic matter delivered during the monsoon period may have already been largely remineralized by the late-to-postmonsoon sampling period. Modelling of porewater O
2 profiles indicates that subsurface O
2 consumption associated oxidation of reduced inorganic species makes a significant contribution to total O
2 consumption at some sites. Similarly, differences in O
2 consumption rates determined by porewater profile modelling and whole-core incubations at some sites indicate significant contributions associated with bioturbation and bioirrigation.

According to Walter Zultowski, senior vice-president of the Life Insurance Marketing & Research Association (LIMRA), the organization will have to keep abreast of the issues that reflect insurers' needs, performance, and problems as the 1990s progress and the 21st century emerges. Over the last decade, LIMRA has been embracing a new philosophy that meets the challenges of an insurance industry in transition. For example, LIMRA has been doing much more interpretation. The organization also is having more contact with member companies, helping them use and understand data. In 1990, LIMRA launched Research 2000, an effort to develop new areas of study to dovetail with existing research programs. LIMRA hopes to broaden its international scope as well.