scholarly journals The protist community mirrors seasonality and mesoscale hydrographic features in the oligotrophic Sargasso Sea

2022 ◽  
Author(s):  
Leocadio Blanco-Bercial ◽  
Rachel Parsons ◽  
Luis Bolaños ◽  
Rod Johnson ◽  
Stephen Giovannoni ◽  
...  
Keyword(s):  
Mixed Layer Depth ◽  
Vertical Position ◽  
Sargasso Sea ◽  
Photic Zone ◽  
Eukaryotic Diversity ◽  
Dynamic Partitioning ◽  
Dna Metabarcoding ◽  
Minimum Zone ◽  
Rapid Transition ◽  
Hydrographic Features

Protists represent the majority of the eukaryotic diversity in the oceans. They have different functions in the marine food web, playing essential roles in the biogeochemical cycles. Meanwhile the available data is rich in horizontal and temporal coverage, little is known on their vertical structuring, particularly below the photic zone. The present study applies DNA metabarcoding to samples collected over three years in conjunction with the BATS time-series to assess marine protist communities in the epipelagic and mesopelagic zones. The protist community showed a dynamic seasonality in the epipelagic, responding to hydrographic yearly cycles. Mixotrophic lineages dominated throughout the year; however, autotrophs bloomed during the rapid transition between the winter mixing and the stratified summer, and heterotrophs had their peak at the end of summer, when the base of the thermocline reaches its deepest depth. Below the photic zone, the community, dominated by Rhizaria, is depth-stratified and relatively constant throughout the year, mirroring local hydrographic and biological features such as the oxygen minimum zone. The results suggest a dynamic partitioning of the water column, where the niche vertical position for each community changes throughout the year, likely depending on nutrient availability, the mixed layer depth, and other hydrographic features. Finally, the protist community closely followed mesoscale events (eddies), where the communities mirrored the hydrographic uplift, raising the deeper communities for hundreds of meters, and compressing the communities above.

scholarly journals Vertical Structure of the Water Column at the Virgin Islands Shelf Break and Trough

2019 ◽  
Vol 7 (3) ◽  
pp. 74
Author(s):  
Giovanni Seijo-Ellis ◽  
David Lindo-Atichati ◽  
Haydee Salmun
Keyword(s):  
Surface Water ◽  
Water Column ◽  
Vertical Structure ◽  
Sea Water ◽  
Mixed Layer Depth ◽  
Virgin Islands ◽  
Shelf Break ◽  
Intermediate Water ◽  
Sargasso Sea ◽  
Subtropical Underwater

The steep US Virgin Islands Shelf Break (VISB) and the Virgin Islands Trough (VIT) at the Northeastern Caribbean Sea comprise a dynamic region of the Atlantic Ocean. In situ oceanographic data collected in the region during April 2017 were used to examine the spatial variability in temperature, density, salinity, and relative Chlorophyll-a. Analysis of data from the upper 300 m of the water column, that include deep and shallow water stations in the shelf break region, shows strong stratification of the water column. Stations shallower than 800 m along the shelf break are more variable in temperature, density, and salinity than those that are deeper than 800 m along the trough. For shallow stations, the mixed layer depth deepens along-shelf from West to East while at the deep stations the opposite occurs. Salinity maxima exhibit more variability in depth and range of values in the shallow stations compared to deep stations. Six different types of water masses that contribute to the strong stratification in the region were identified in our study: Caribbean Surface Water, Subtropical Underwater, Sargasso Sea Water, Tropical Atlantic Central Water, Antarctic Intermediate Water, and North Atlantic Deep Water. The upper level Caribbean Surface Water, Subtropical Underwater, and Sargasso Sea Water are present in shallow stations, indicating potential meridional intrusions from the VIT to the VISB which may not be resolved by current ocean circulation models and are not captured in satellite data. The analysis presented here indicates that competing physical processes may be controlling the vertical structure of the water column in the region and merit further examination.

scholarly journals The oceanic non-sulfidic oxygen minimum zone: a habitat for graptolites?

1987 ◽  
Vol 35 ◽  
pp. 103-114 ◽  
Author(s):  
William B. N. Berry ◽  
Pat Wilde ◽  
Mary S. Quinby-Hunt
Keyword(s):  
Food Supply ◽  
Photic Zone ◽  
Early Paleozoic ◽  
Low Oxygen ◽  
Potential Habitat ◽  
Living Space ◽  
Deep Waters ◽  
Mode Of Life ◽  
Minimum Zone ◽  
Oxygen Minimum

The denitrified low oxygen zone in Early Paleozoic oceans is proposed as a potential habitat of planktic graptolites. Modern analogs of this zone are found in the eastern tropical Pacific (ETP) and in the north­ern Arabian Sea as shallow regions, up to a 100 meters thick, at the top of the pycnocline. There, oxygen is low or undetected and hydrogen sulfide has not been found. In modem oceans, denitrification regions are limited vertically and horizontally as oxygen is replenished from below by ventilated deep waters. In the Early Paleozoic ocean, the denitrification layer would be global due to poor deep ventilation. It would be transitional between oxygenated surface waters and toxic sulfide-rich water. Many branched graptolites could have evolved when the denitrified waters were in or close to the photic zone, feeding on the abun­dant phytoplankton attracted to both light and nutrients. As this zone sank below the photic zone, grapto­lites who developed planktic mode of life could have migrated daily toward the food supply, similar to euphausiids in the modern ETP. Thus the changes in graptolite rhabdosomes from pendent to scandent and from many branched to biserial and uniserial are suggested as adaptations to assist vertical migration and feeding. With the continued ventilation of the oceans and the shrinking of the denitrified layer, grap­tolite extinction could have resulted as a combination of reduction in food supply and living space, in­creased predation from the then evolving fish and ammonites, and competition in the zoop!ankton niche from smaller (less visible) and more motile forms.

Using Synthetic Brightness Temperatures to Address Uncertainties in Cloud-Top-Height Verification

2017 ◽  
Vol 56 (2) ◽  
pp. 283-296
Author(s):  
Jason E. Nachamkin ◽  
Yi Jin ◽  
Lewis D. Grasso ◽  
Kim Richardson
Keyword(s):  
North Atlantic ◽  
North Atlantic Ocean ◽  
Deep Convection ◽  
Vertical Position ◽  
Sargasso Sea ◽  
Ice Clouds ◽  
Brightness Temperatures ◽  
The North ◽  
Common Problems ◽  
Cloud Tops

AbstractCloud-top verification is inherently difficult because of large uncertainties in the estimates of observed cloud-top height. Misplacement of cloud top associated with transmittance through optically thin cirrus is one of the most common problems. Forward radiative models permit a direct comparison of predicted and observed radiance, but uncertainties in the vertical position of clouds remain. In this work, synthetic brightness temperatures are compared with forecast cloud-top heights so as to investigate potential errors and develop filters to remove optically thin ice clouds. Results from a statistical analysis reveal that up to 50% of the clouds with brightness temperatures as high as 280 K are actually optically thin cirrus. The filters successfully removed most of the thin ice clouds, allowing for the diagnosis of very specific errors. The results indicate a strong negative bias in midtropospheric cloud cover in the model, as well as a lack of land-based convective cumuliform clouds. The model also predicted an area of persistent stratus over the North Atlantic Ocean that was not apparent in the observations. In contrast, high cloud tops associated with deep convection were well simulated, as were mesoscale areas of enhanced trade cumulus coverage in the Sargasso Sea.

scholarly journals Oceanic changes in the Sargasso Sea and declines in recruitment of the European eel

2007 ◽  
Vol 64 (3) ◽  
pp. 519-530 ◽  
Author(s):  
Kevin D. Friedland ◽  
Michael J. Miller ◽  
Brian Knights
Keyword(s):  
North Atlantic ◽  
Mixed Layer Depth ◽  
Life Stage ◽  
Larval Survival ◽  
Larval Transport ◽  
Anthropogenic Factors ◽  
European Eel ◽  
Sargasso Sea ◽  
The North ◽  
The North Atlantic

Abstract Friedland, K. D., Miller, M. J., and Knights, B. 2007. Oceanic changes in the Sargasso Sea and declines in recruitment of the European eel. – ICES Journal of Marine Science, 64: 519–530. Anguillid eel recruitment in the North Atlantic has declined in recent decades, raising concerns that climatic changes in the Sargasso Sea may be influencing oceanic reproduction and larval survival. There is a significant negative correlation between the North Atlantic Oscillation and long-term variations in catches of glass eel stages of the European eel Anguilla anguilla recorded by the fishery independent Den Oever recruitment index (DOI) in the Netherlands, lagged by one year. Ocean-atmospheric changes in the Sargasso Sea may affect the location of spawning areas by silver eels and the survival of leptocephali during the key period when they are transported towards the Gulf Stream. A northward shift in a key isotherm (22.5°C), defining the northern boundary of the spawning area, a declining trend in winds and transport conditions in larval transport areas, and a shallowing of the mixed layer depth could affect primary productivity in areas where leptocephali feed. The relationships between these ocean parameters and the DOI suggest that these changing ocean conditions could be contributing to declining recruitment of the European eel and probably also of the American eel (A. rostrata), but anthropogenic factors during their continental life stage must also be considered.

Temporally invariable bacterial community structure in the Arabian Sea oxygen minimum zone

2014 ◽  
Vol 73 (1) ◽  
pp. 51-67 ◽  
Author(s):  
A Jain ◽  
M Bandekar ◽  
J Gomes ◽  
D Shenoy ◽  
RM Meena ◽  
...  
Keyword(s):  
Community Structure ◽  
Bacterial Community ◽  
Bacterial Community Structure ◽  
Arabian Sea ◽  
Oxygen Minimum Zone ◽  
Minimum Zone ◽  
Oxygen Minimum
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