Southern Ocean waters have been identified as critical regions because of their potential to impact global climate as they play an integral role in oceanic overturning and circulation. They are also an area of deep and intermediate water formation and can potentially modulate atmospheric CO 2 concentrations. This project focuses on two regions that are seasonally limited by biologically available iron, the open HNLC Southern Ocean and the Ross Sea. The objective of this project was to determine how iron impacts the regulation of photosystem II and how the presence of particular phytoplankton species affects the ability of satellites to estimate biomass from remote sensing of ocean color. Two pulse amplitude modulated fluorometers were used to examine the photochemical efficiency of whole phytoplankton assemblages and single cells in both iron enrichment experiments and during a natural phytoplankton bloom in the Ross Sea from 2001--04. There were no significant differences in the photochemical recoveries of diatoms during the Southern Ocean Iron Experiment, with exception of Asteromphalus sp. (a centric diatom). The kinetics of increase from iron stress suggested that they occurred independently of cell surface area. A relationship between diatom abundance and SeaWiFS overestimation of chlorophyll a in the eastern Ross Sea was found in 2001--2, but this trend was not observed in other years when diatoms dominated. Under most circumstances (phytoplankton composition and size distribution), it appears that with a linear post-calibration correction we could utilize SeaWiFS for phytoplankton biomass estimates in the Ross Sea. However, we could not explain the degree that SeaWiFS over- or underestimated the in situ chlorophyll a with taxonomic composition or phytoplankton size distribution. There was distinct interannual variability in the Ross Sea over the course of our three year study. In February 2003 there was a clear secondary bloom dominated by diatoms, a feature previously unreported in the central Ross Sea. Intrusions of modified circumpolar deep water regulated the timing and magnitude of the second diatom bloom in 2003--2004 by infusing surface waters with additional iron. We could not conclusively explain the spatial variability in the phytoplankton assemblage with the fluorescence-based light utilization parameters or the mixed layer depth.

No description available.

The demersal fish community of the outer continental shelf in the Middle Atlantic Bight consists of resident species, seasonal species with boreal affinities, and seasonal species with warm temperature affinities. Dominant demersal fishes of the outer continental shelf feed primarily on macrobenthic invertebrates, which persist in dense, stable communities. Some dominant predators also feed heavily on fishes, cephalopods, and planktonic invertebrates, at least seasonally. Food habits of the fishes change seasonally, especially at the species level. Food habits of fishes also change considerably with size, with most predators showing distinct feeding stanzas separated by a marked change in feeding strategy. Electivity patterns of predators upon the benthos were varied with respect to prey distribution and abundance patterns. Some dominant benthic species were not selected as food. Other rarer species were preferentially selected. Some prey species that varied in abundance with respect to habitat strata were eaten in proportion to their abundance in most habitats. Others were eaten only where very abundant, or were consumed in moderate amounts regardless of their abundance in the benthos. Several factors may account for these patterns. Most predator species shared many prey species. Overlap in diet among the predators varied seasonally, with overlap relationships changing as species and size class composition of the predators changed. Intra-specific diet overlap between feeding stanzas was low, but higher interspecific overlap occurred between species of similar size. Dietary overlap was lowest in the spring, when planktonic and nektonic organisms were consumed by most size classes of dominant predators. Although many important prey species were consumed by several predators, some were selectively consumed by only a few predators, so that there was never complete dietary overlap between two species.

No description available.

Zooplankton play an important role in global biogeochemistry and their secondary production supports valuable fisheries of the world’s oceans. Coupled physical-biogeochemical models (PBMs) provide a unique oceanographic research tool for studying zooplankton on basin and global scales since zooplankton cannot currently be estimated using remote sensing techniques. However, evaluating the accuracy of zooplankton abundance estimates from PBMs has been a major challenge as a result of sparse ship-based observations. Consequently, zooplankton dynamics have been under studied and under validated in PBMs. In this study, we configure a PBM for the Gulf of Mexico (GoM) and validate simulated zooplankton fields against an extensive combination of in situ biomass and rate measurements. We find that spatial variability in mesozooplankton biomass observed in a multi-decadal database for the northern GoM is well resolved by the model with a statistically significant (p < 0.05) correlation of 0.74. In terms of community composition, the model estimates that large zooplankton (LZ) and predatory zooplankton (PZ) functional groups makes up approximately 40% and 60% of the simulated mesozooplankton biomass respectively, which is further supported by ship-based measurements. Once validated the model was used to investigate mesozooplankton diet and secondary production. Model results of LZ dietary composition suggests that herbivory is the dominant feeding pathway whereas PZ dietary composition is largely carnivorous. Dietary composition is found to be less binary in the oligotrophic GoM where LZ and PZ feed on a combination of phytoplankton and zooplankton. We discuss how already low mesozooplankton biomass in the oligotrophic Gulf (~0.04 mmol N m-3) may become further reduced in the future with important impacts on food availability for higher planktivorous trophic levels such as pelagic larval fish. Such reductions could be expected from increases in thermal stratification as a result of a warming ocean and ensuing increases in bottom-up ecosystem limitation. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2019. / April 17, 2019. / bio-physical model, Gulf of Mexico, larval fish, offline modeling, physical-biogeochemical model, zooplankton / Includes bibliographical references. / Michael Stukel, Professor Co-Directing Thesis; Eric Chassignet, Professor Co-Directing Thesis; Steven Morey, Committee Member; Sven Kranz, Committee Member; Nicholas Cogan, Committee Member.

Stable hydrogen and carbon isotopic compositions of biogenic methanes collected from the sediments of several deep-sea, nearshore marine-estuarine, and freshwater environments were determined. The isotopic compositions of methane samples from eight different DSDP Sites (mean σD-CH4 = -1850>/∞, std. dev. = 70>/∞, n = 75; mean σ13C-CH4 = -71.30/∞, std. dev. = 6.30/∞, n = 44) are generally typical of methane formed via C02 reduction in deep-sea sediments. Methane collected from several freshwater environments was D-depleted (mean σD-CH4 = -3000>/∞ , std. dev. = 260/∞, n = 20) and 13C-enriched (mean σ13C-CH4 = -60.10/∞, std. dev. = 6.10/∞, n = 20) compared to the deep-sea methane. Normally, acetate dissimilation is thought to account for about 60 to 70% of the total methane production in freshwater sediments. Nearshore marine-estuarine methanes appear to be isotopically intermediate (mean σD-CH4 = -2580>/∞ , std. dev. = 230/∞, n = 46; σ13C-CH4 = -61.80/∞, std. dev. = 3.10/∞, n = 46) between deep-sea and freshwater methanes. Variation in the relative importance of the two main methanogenic pathways, acetate dissimilation and C02 reduction, is probably the single most important factor responsible for the differences in methane isotopic compositions among these three different types of environments. Other factors that probably contribute to the methane isotopic differences are temperature, sedimentation rate, organic matter type and amount, concentration of alternate electron acceptors, rate of methane formation and possibly postgenerative isotopic equilibration. Shallow aquatic sediments are thought to be an important source of methane to the atmosphere; the methane produced in these systems, including the ones sampled in this study, is generally substantially more 13C-depleted than expected based on the σ13C of atmospheric methane and the isotopic fractionation associated with the atmospheric sink process. Too few oD data are available to allow evaluation of the role of shallow aquatic sediments in determining atmospheric σD-CH4.

In the shallow, bar-built estuary Apalachicola Bay, the discharge of the Apalachicola River, the largest river in Florida by discharge volume, produces short residence times of water in the Bay and pronounced gradients in salinity and nutrients. This, in combination with wind- and tidal-driven circulation, generates an environment for plankton that is complex and highly dynamic. Understanding these dynamics and the factors controlling them is prerequisite for estimating phytoplankton biomass and productivity in such ecosystems. This research assessed the variability of estuarine phytoplankton in Apalachicola Bay at multiple temporal and spatial scales, utilizing high resolution spatial sampling, dye release experiments monitored with a drone, and a long-term record of water quality. Small-scale chlorophyll a (Chl a) peaks (1.3 ± 0.7 km wide) had steep gradients (3.0 ± 6.0 µg Chl a L-1 km-1) and accounted for 7.7 ± 2.7 % of the biomass observed with a flow-through water quality instrument. Winds, tides, and temperature affected Chl a peak characteristics, while the river plume front was a dynamic location of elevated Chl a. Horizontal dispersion of small-scale inert tracer patches (10-100 m) were faster than phytoplankton reproduction cycles, suggesting that small-scale phytoplankton patches may not be able to outpace physical dispersion in estuaries through growth. The evaluation of a 14-year time series of bay water quality data revealed that extreme river discharge events influenced intra- and interannual variability of Chl a. The nutrient buffering capacity of Apalachicola Bay, in conjunction with longer residence time, increased light penetration, and reduced grazing pressure, may mitigate the reduction of riverine nutrient input during drought. In contrast, tropical storms and high river discharge events may lead to periods of reduced phytoplankton biomass by increasing flushing rates of the estuary and reducing light availability. These new insights into the spatial and temporal variability of phytoplankton distribution and what’s controlling it helps coastal managers to understand how river discharge, winds, and tides affect biomass in bar-built estuaries. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester 2017. / April 13, 2017. / Drought, Estuaries, Phytoplankton, Rhodamine WT, River, Spatial variability / Includes bibliographical references. / Markus Huettel, Professor Directing Dissertation; Thomas Miller, University Representative; Michael Wetz, Committee Member; Kevin Speer, Committee Member; William Landing, Committee Member.

Thesis (Ph.D.) in Marine Biology--University of Maine, 2006. / Includes vita. Includes bibliographical references (leaves 218-228).

Graduation date: 1978

A mooring system was designed and constructed to make possible the installation and the recovery of racks of sample panels for a study of deep-ocean wood-boring molluscs. Racks containing pine, fir, oak, and cedar boards were exposed to borer attack at six stations with depths of 50, 100, 150, 200, 500 and 1000 meters, all west of Depoe Bay, Oregon. Two wood-boring molluscs, a pholad, Xylophaga washingtona Bartsch, and a teredinid, Bankia setacea (Tyron), were recovered from exposed wood materials. Xylophaga washingtona was the dominant form and was found at all three deep stations. Bankia setacea was found only at the 200-meter site and in very low numbers. This reports the deepest known teredinid actively settling and boring into a test board. Borer attack increased in intensity with time, and in general, decreased with increasing depth. Initial attack appeared to commence right above the line where sample panels were in contact with the sediment. Attack was heaviest in this zone and decreased with increasing distance upward from the sea-sediment interface, approaching zero in about 20 centimeters. In general cedar was the most heavily attacked wood type followed in turn by pine, fir, and then oak, which proved the most resistant to xylophagan borers, The degree of maximum borer penetration into any wood type correlated nicely with the density of the wood, higher density wood being correspondingly most resistant to borer attack. Degree of maximum borer penetration increased with time and decreased with increasing depth. The mooring system is fully described along with a summary of field installation and recovery methods. Future research problems are suggested. / Graduation date: 1968