262 research outputs found
Ocean color, a three component system?
This study measures the concentrations of phytoplankton chlorophyll and yellow substance in the coastal waters of the Gulf of Maine. Sea surface observations attempt to delineate the principal biochemical parameters responsible for sea surface color. It is shown that the reddish-brown water changed to a blue-green in the open gulf
Seasonal sequence of bioluminescence and the occurrence of endogenous rhythms in oceanic waters off Woods Hole, Massachusetts
Seasonal sequences of bioluminescense in waters around Woods Hole were measured in 1961 to 1963. Peak activities occurred in October-November (once) and in April-May (twice). Bioluminescense at night is usually quantitatively greater than during the day. Greater differences during summer correlate with the seasonal maximum in solar radiation...
Grazer control of the fine-scale distribution of phytoplankton in warm-core Gulf Stream rings
We measured in situ rates of primary production, zooplankton grazing and the fine-scale distribution of zooplankton abundance, along with continuous observations of salinity, temperature and fluorescence in vertical profiles of two warm-core Gulf Stream rings and a station in the northern Sargasso Sea. A subsurface chlorophyll maximum was located within the pycnocline at all nineteen of the pump stations. In the majority of pump profiles, subsurface chlorophyll maxima coincided with maxima in particulate organic carbon and ATP. However, neither zooplankton biomass or numerical abundance were related to chlorophyll concentrations. Maxima in zooplankton biomass and grazing generally occurred at depths of highest primary production. Zooplankton grazing and biomass were more closely coupled to phytoplankton production per unit chlorophyll (P-chl) rather than production per unit volume (absolute production). Our results suggest that after the seasonal thermocline is established, phytoplankton removal by zooplankton is greatest in the upper water column where P-chl is higher. This phytoplankton removal by zooplankton limits the amount of absolute primary production in the upper water column and results in a subsurface maximum of absolute production at depths where grazing pressure is reduced. In contrast, the subsurface chlorophyll maximum, likely formed from both production at depth and sinking, does not appear to be a site of enhanced zooplankton grazing activity
Chronic Exposure of Corals to Fine Sediments: Lethal and Sub-Lethal Impacts
Understanding the sedimentation and turbidity thresholds for corals is critical in assessing the potential impacts of dredging projects in tropical marine systems. In this study, we exposed two species of coral sampled from offshore locations to six levels of total suspended solids (TSS) for 16 weeks in the laboratory, including a 4 week recovery period. Dose-response relationships were developed to quantify the lethal and sub-lethal thresholds of sedimentation and turbidity for the corals. The sediment treatments affected the horizontal foliaceous species (Montipora aequituberculata) more than the upright branching species (Acropora millepora). The lowest sediment treatments that caused full colony mortality were 30 mg lâ1 TSS (25 mg cmâ2 dayâ1) for M. aequituberculata and 100 mg lâ1 TSS (83 mg cmâ2 dayâ1) for A. millepora after 12 weeks. Coral mortality generally took longer than 4 weeks and was closely related to sediment accumulation on the surface of the corals. While measurements of damage to photosystem II in the symbionts and reductions in lipid content and growth indicated sub-lethal responses in surviving corals, the most reliable predictor of coral mortality in this experiment was long-term sediment accumulation on coral tissue
The influence of phytoplankton composition on the relative effectiveness of grinding and sonification for chlorophyll extraction
The chlorophyll recovery efficiency was compared between control, ground, and sonified samples. The results showed significant improvement between control and ground samples but not between control and sonified samples. Neither prolonging time of sonification nor using an ice bath during filter grinding improved efficiency. Higher chlorophyll a recovery was obtained from ground samples than from sonified ones, when the water samples contained centric diatoms and filamentous blue-green algae. When total phytoplankton numbers were high, there was a distinct advantage in using grinding rather than sonification for chlorophyll c recovery.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42913/1/10750_2004_Article_BF00008504.pd
Stoichiometry of the degradation of dissolved and particulate biogenic organic matter in the NW Iberian upwelling
The average composition of the dissolved and particulate products of early
degradation of marine phytoplankton has been established for the first time in a coastal
upwelling system using a mixing analysis along isopycnal surfaces combined with a
stoichiometric model. About 17â18% of the mineralized organic matter is derived
from the decomposition of organic particulates, and 16â35% is from the dissolved
organic matter. The remaining 50â70% is derived probably from large fast sinking
particles. On average, the mineralized material on large particles has the closest
composition to the Redfield formula. The ratio of dissolved saccharides to dissolved
organic matter respiration is >40% higher than expected from a material of Redfield
composition. Finally, the ratio of lipid to particulate organic matter respiration is >80%
larger than expected from a material of Redfield composition. Regarding the
decomposition of hard structures, biogenic silica dissolves predominantly in the inner
shelf, where organic carbon oxidation is more intense, and diatom deposition occurs
preferentially
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