Richard L. Iverson

Dimethylsulfide and Phaeocystis poucheti in the southeastern Bering Sea

Abstract Dimethylsulfide (DMS), a volatile excretion product of marine phytoplankton, was determined in the water column during the spring phytoplankton bloom on the southeastern Bering Sea shelf. In the same samples, a broad range of variables which characterize the biological processes in this region were measured. DMS was correlated with phytoplankton chlorophyll in the outer shelf and oceanic domains, but not in the middle shelf domain. A very strong correlation between the cell density of the haptophyte Phaeocystis poucheti and the DMS concentration in seawater was found, which suggests that this species accounts for most of the DMS present in the study region. We propose that in P. poucheti and certain other phytoplankton species the excretion of DMS is incidental to the release of acrylic acid which serves to inhibit bacterial attack upon the algae.

Exudation of organic carbon by the seagrass Halodule wrightii Aschers. and its effect on bacterial growth in the sediment

Abstract Between 6 and 28% (mean: 14%) of 14 C fixed by the leaves of Halodule wrightii Aschers, was translocated to the rhizomes and roots within 6 h. In the same time period 6 to 17% (mean: 11%) of total fixed 14 C was exuded into the sediment. About 1% was excreted into the water column. Bacterial production was determined using two methods: the rate of tritiated thymidine incorporation into DNA and the rate of 32 P incorporation into phospholipid. Bacterial production was 180 to 190mg C · m −2 · day −1 and was probably dependent on root decomposition as well as exudation. From the results of lipid analyses and synthesis it was concluded that bacteria were utilizing all the exuded organic 14 C. Most bacterial production was in the top 20 mm of sediment, which was the zone with the greatest root and rhizome biomass. Most of the 14 C exudate was also found in this zone.

Seagrass distribution and abundance in Eastern Gulf of Mexico coastal waters

The marine angiosperms Thalassia testudinum, Syringodium filiforme, and Halodule wrightii form two of the largest reported seagrass beds along the northwest and southern coasts of Florida where they cover about 3000 square km in the Big Bend area and about 5500 square km in Florida Bay, respectively. Most of the leaf biomass in the Big Bend area and outer Florida Bay was composed of Thalassia testudinum and Syringodium filiforme which were distributed throughout the beds but which were more abundant in shallow depths. A short-leaved form of Halodule wrightii grew in monotypic stands in shallow water near the inner edges of the beds, while Halophila decipiens and a longer-leaved variety of H. wrightii grew scattered throughout the beds, in monotypic stands near the outer edges of the beds, and in deeper water outside the beds. Halophila engelmanni was observed scattered at various depths throughout the seagrass beds and in monospecific patches in deep water outside the northern bed. Ruppia maritima grew primarily in brackish water around river mouths. The cross-shelf limits of the two major seagrass beds are controlled nearshore by increased water turbidity and lower salinity around river mouths and off-shore by light penetration to depths which receive 10% or more of sea surface photosynthetically active radiation. Seagrasses form large beds only along low energy reaches of the coast. The Florida Bay seagrass bed contained about twice the short-shoot density of both Thalassia testudinum and Syringodium filiforme, for data averaged over all depths, and about four times the average short-shoot density of both species in shallow water compared with the Big Bend seagrass bed. The differences in average seagrass abundance between Florida Bay and the Big Bend area may be a consequence of the effects of greater seasonal solar radiation and water temperature fluctuations experienced by plants in the northern bed, which lies at the northern distribution limit for American Tropical seagrasses.

Estuarine and Plume Fronts

In this chapter we discuss the properties and dynamics of small scale fronts with length and time scales of the order of the tidal excursion and period. Such fronts are commonly found in estuaries and shallow seas.

Does the marine biosphere mix the ocean

Ocean mixing is thought to control the climatically important oceanic overturning circulation. Here we argue the marine biosphere, by a mechanism like the bioturbation occurring in marine sediments, mixes the oceans as effectively as the winds and tides. This statement is derived ultimately from an estimated 62.7 TeraWatts of chemical power provided to the marine environment in net primary production. Various approaches argue something like 1% (.63 TeraWatts) of this power is invested in aphotic ocean mechanical energy, a rate comparable to wind and tidal inputs.

The effect of groundwater seepage on nutrient delivery and seagrass distribution in the northeastern Gulf of Mexico

A hypothesis was tested to determine if a relationship exists between rates of submarine groundwater discharge and the distribution of seagrass beds in the coastal, nearshore northeastern Gulf of Mexico. As determined by nonparametric statistics, four of seven seagrass beds in the northeastern Gulf of Mexico had significantly greater submarine groundwater discharge compared with adjacent sandy areas, but the remainder exhibited the opposite relationship. We were thus unable to verify if a relationship exists between submarine groundwater discharge and the distribution of seagrass beds in the nearshore sites selected. A second objective of this study was to determine the amount of nitrogen and phosphorus delivered to nearshore areas by submarine groundwater discharge. We considered new nutrient inputs to be delivered to surface waters by the upward flux of fresh water. This upward flux of water encounters saline porewaters in the surficial sediments and these porewaters contain recycled nutrients; actual nutrient flux from the sediment to overlying waters includes both new and recycled nutrients. New inputs of nitrogen to overlying surface waters for one 10-km section of coastline, calculated by multiplying groundwater nutrient concentrations from freshwater wells by measured seepage rates, were on the order of 1,100±190 mol N d−1. New and recycled nitrogen fluxes, calculated by multiplying surficial porewater concentrations by measured seepage rates, yielded fluxes of 3,600 ±1,000 mol N d−1. Soluble reactive phosphate values were 150±40 mol P d−1 using freshwater well concentrations and 130±3.0 mol P d−1 using porewater concentrations. These values are comparable to the average nutrient delivery of a small, local river.

The influence of seagrass beds on carbonate sediments in the Bahamas

Chemical variables were measured in calcium-carbonate-rich sediments inhabited by the dominant tropical seagrass, Thalassia testudinum, and in adjacent seagrass-free sediments at several locations in the Bahamas Islands. Pore-water alkalinity and pCO2 were consistently greater, while pH was consistently lower in sediment-pore waters within seagrass beds. The ammonium and molybdate-reactive phosphate concentrations in sediment-pore water were variable for vegetated, compared with unvegetated, sample locations. Thalassia testudinum can generate very large amounts of organic matter within calcium-carbonate-rich sediments. However, little of the organic matter is retained in the sediment and the effect of that organic matter on pore water chemical factors appears to be surprisingly small. These observations are markedly different from those for seagrass beds in high latitude clastic sediments and in Syringodium filiforme seagrass beds near San Salvador Island, where major influences of the seagrass beds on sediment chemistry have been observed. The generally coarser grain size of the carbonate sediments may be a primary factor contributing to these differences.

The effect of salinity and dissolved organic matter on surface charge characteristics of some euryhaline phytoplankton

Abstract The effects of salinity and dissolved organic matter upon the surface charge characteristics of selected phytoplankton were investigated by means of microelectrophoresis. Nannochloris oculata Droop, Monochrysis lutheri Droop, and Cyclotella meneghiniana Kutzing, were negatively charged in diluted sea water. The magnitude of the electrophoretic mobility (EPM) of two of the phytoplankton species decreased as the salinity of the medium increased. Heat killing influenced the EPMs of the three phytoplankton species, suggesting the possibility that the surface charge of these phytoplankton organisms is influenced by surface biological processes. The EPM of C. meneghiniana decreased when the dissolved organic content of the medium was greater than 0.3 mg/1. Dissolved humic acids also inhibited the rate and magnitude of mercury sorption by C. meneghiniana .

The effects of convective and wind-driven mixing on spring phytoplankton dynamics in the Southeastern Bering Sea middle shelf domain

Abstract Spring phytoplankton bloom conditions for the southeastern Bering Sea shelf were simulated with a coupled phytoplankton-nutrient-detritus model that received input from a physical mixed-layer model. The models captured the essential features of chlorophyll, dissolved inorganic nitrogen concentration, and temperature fields during the spring bloom onset and progression in 1980 and 1981. In contrast to critical depth theory, the occurrence of a shallow mixed-layer depth and a period of low wind speed were not sufficient to trigger the spring bloom. In both years, the spring bloom onset occurred in response to the cessation of convective mixing during a period of increasing atmospheric temperature and decreasing wind speed. Differences between 1980 and 1981 post-spring-bloom characteristics, however, resulted from differences in water column stability, and wind speed variability and magnitude through time. Those factors affected the vertical distributions of nitrogen and chlorophyll, and, therefore, phytoplankton growth rate. A high degree of model accuracy was indicated by low average RMSE values for euphotic zone model variable values compared to data. This was a consequence of the dominant role that meteorological forcing had on variable fields and processes during spring 1980 and 1981, and the application of a physical model that was specifically designed to model vertical mixing processes.

Uptake of glycolic acid by a marine bivalve

Abstract Glycolic acid is accumulated by in vitro preparations of gill tissue from the quahog clam, Mercenaria sp., by a process indicating diffusion kinetics. Carbon-14 from labelled glycolic acid was found in the lipid fraction of the gill tissue. Evolution of labelled carbon dioxide suggests that the glycolic acid is metabolized in gill tissue.