YOUNGER DRYAS MARINE ECOSYSTEM RECORD FROM SITKA SOUND ALASKA, USA: RAPID TRANSITION FROM PROGLACIAL LAKE TO OPEN OCEAN

Abstract. Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg−1) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg−1. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day−1, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

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Timing and duration of North American glacial lake discharges and the Younger Dryas climate reversal

Quaternary Research ◽

10.1016/j.yqres.2011.02.004 ◽

2011 ◽

Vol 75 (3) ◽

pp. 541-551 ◽

Cited By ~ 35

Author(s):

John A. Rayburn ◽

Thomas M. Cronin ◽

David A. Franzi ◽

Peter L.K. Knuepfer ◽

Debra A. Willard

Keyword(s):

Ocean Circulation ◽

North Atlantic ◽

North American ◽

Younger Dryas ◽

Ice Cores ◽

Cold Event ◽

Lawrence Estuary ◽

The North ◽

The North Atlantic ◽

Proglacial Lake

AbstractRadiocarbon-dated sediment cores from the Champlain Valley (northeastern USA) contain stratigraphic and micropaleontologic evidence for multiple, high-magnitude, freshwater discharges from North American proglacial lakes to the North Atlantic. Of particular interest are two large, closely spaced outflows that entered the North Atlantic Ocean via the St. Lawrence estuary about 13,200–12,900 cal yr BP, near the beginning of the Younger Dryas cold event. We estimate from varve chronology, sedimentation rates and proglacial lake volumes that the duration of the first outflow was less than 1 yr and its discharge was approximately 0.1 Sv (1 Sverdrup = 106 m3 s−1). The second outflow lasted about a century with a sustained discharge sufficient to keep the Champlain Sea relatively fresh for its duration. According to climate models, both outflows may have had sufficient discharge, duration and timing to affect meridional ocean circulation and climate. In this report we compare the proglacial lake discharge record in the Champlain and St. Lawrence valleys to paleoclimate records from Greenland Ice cores and Cariaco Basin and discuss the two-step nature of the inception of the Younger Dryas.

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Shelf ecosystem response to the Eocene-Oligocene Transition

10.5194/egusphere-egu2020-1053 ◽

2020 ◽

Author(s):

Laura Cotton ◽

David Evans ◽

Daniela Schmidt

Keyword(s):

High Resolution ◽

Environmental Change ◽

Trace Element ◽

Marine Ecosystem ◽

Marine Ecosystems ◽

Open Ocean ◽

Ecosystem Dynamics ◽

Ecosystem Response ◽

Holistic View ◽

Shallow Marine

The Eocene-Oligocene transition (EOT) is one of the most dramatic climate shifts of the Cenozoic with severe consequences for reef ecosystems. The onset of continental Antarctic glaciation is associated with widespread environmental change, resulting in a global peak in biotic turnover. Whilst numerous studies of the biotic response to the changes at the EOT have been carried out, most high-resolution studies consist of open ocean records of marine plankton and predominantly single groups of organisms. However, this is not representative of the ocean system as a whole and does not provide a holistic view of mechanism of restructuring of the marine ecosystems. The shelf seas and reefs are some of the most diverse and fundamentally important ecosystems of the oceans. Long-term diversity loss across the EOT has been shown in several macrofossil studies, but mainly at low resolution, and recovery is not well understood.&#160; Many shelf species are ecosystem engineers whose loss and recovery have profound implications for the entire ecosystem. Understanding these interactions will provide insights into shallow marine ecosystems and their response to major climate perturbations.The Tanzanian Drilling Project EOT record (TDP 11, 12, 17) is recognised globally for its completeness and exceptionally preserved calcareous microfossils. It is most importantly, though, a rare record of both shallow water organisms and open ocean plankton. The latter are fundamentally important for reconstructions of the environment and a globally calibrated timescale. Here we draw together a unique dataset of high-resolution mollusc, Dasycladaceae, bryozoan, larger benthic foraminifers, coral, smaller benthic foraminifera, trace element and isotope records from the EOT. The response and recovery of these species is compared with known, modern physiology of each group to provide a complete picture of the shallow marine ecosystem response.Following rapid extinctions within the larger foraminifera during the transition, molluscs, Dasycladaceae and bryozoans all show increases in abundance, indicating a major shift in shelf ecosystem composition. These assemblage changes are coincident with a period of more positive values in d13C of both benthic and planktonic foraminifera and changes in trace element values. Comparison with the open ocean record of planktonic foraminiferal, pteropod, and nannofossils confirm these assemblage changes are a biological, rather than sedimentological response and additionally support a that a transition to more eutrophic conditions took place.&#160;an environmental framework of traditional and novel geochemistry, indicate that increased nutrient fluxes played a pivotal role in restructuring shelf ecosystem dynamics and therefore offers new insight into mechanisms of reorganisation under ecosystem loss and environmental change.

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Editorial: The Azores Marine Ecosystem: An Open Window Into North Atlantic Open Ocean and Deep-Sea Environments

Frontiers in Marine Science ◽

10.3389/fmars.2020.601798 ◽

2020 ◽

Vol 7 ◽

Author(s):

Telmo Morato ◽

Pedro Afonso ◽

Gui M. Menezes ◽

Ricardo S. Santos ◽

Mónica A. Silva

Keyword(s):

North Atlantic ◽

Deep Sea ◽

Marine Ecosystem ◽

Open Ocean ◽

Open Window

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On the connection between coastal Ekman upwelling and wind-stress-curl-driven upwelling off the southwest African coasts

10.5194/egusphere-egu21-12206 ◽

2021 ◽

Author(s):

Mohammad Hadi Bordbar ◽

Volker Mohrholz ◽

Martin Schmidt

Keyword(s):

Chlorophyll A ◽

Wind Stress ◽

Coastal Upwelling ◽

Model Simulation ◽

Marine Ecosystem ◽

Phase Relationship ◽

Open Ocean ◽

Wind Stress Curl ◽

Upwelled Water ◽

Ekman Theory

Spatial and temporal variations of nutrient-rich upwelled water across the major eastern boundary upwelling systems are primarily controlled by the surface atmospheric flow with different, and sometimes contrasting, impacts on coastal and open-ocean upwelling systems. Here, concurrently measured wind-fields, satellite-derived Chlorophyll-a concentration along with a state-of-the-art ocean model simulation spanning 2008-2018 are used to investigate the connection between coastal and offshore physical drivers of the Benguela Upwelling System (BUS). Our results indicate that the spatial structure of long-term mean upwelling derived from Ekman theory and the numerical model are fairly consistent across the entire BUS and closely followed by the Chlorophyll-a pattern. The variability of the upwelling from the Ekman theory is proportionally diminished with offshore distance, whereas different and sometimes opposite structures are revealed in the model-derived upwelling. Our result suggests the presence of sub-mesoscale activity (i.e. filaments and eddies) across the entire BUS with a large modulating effect on the wind-stress-curl-driven upwelling off L&#252;deritz and Walvis Bay. In Kunene and Cape Frio upwelling cells, located in the northern sector of the BUS, the coastal upwelling and open-ocean upwelling frequently alternate each other, whereas they are modulated by the annual cycle and mostly in phase off Walvis Bay. Such a phase relationship appears to be strongly seasonal dependent off L&#252;deritz and across the southern BUS. Thus, our findings suggest this relationship is far more complex than currently thought and seems to be sensitive to climate changes with short- and far-reaching consequences for this vulnerable marine-ecosystem.

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A unique winged euthycarcinoid from the Permian of Antarctica

Journal of Paleontology ◽

10.1017/jpa.2017.28 ◽

2017 ◽

Vol 91 (5) ◽

pp. 987-993

Author(s):

Joseph H. Collette ◽

John L. Isbell ◽

Molly F. Miller

Keyword(s):

Fossil Record ◽

Trace Fossil ◽

Morphological Similarity ◽

Evolutionary Transitions ◽

Body Segments ◽

Rapid Transition ◽

Proglacial Lake ◽

High Degree ◽

Freshwater Environments

AbstractEuthycarcinoid arthropods (Cambrian–Triassic) were likely the first animals to transition from oceanic to freshwater and emergent environments. Although their basic bauplan is well known, they have a poor fossil record because their non-sclerotized exoskeleton was rarely preserved. Euthycarcinoids’ unusual morphology (varying numbers of body segments, seemingly dichotomous possession of either mandibles or a labrum, specialized or generalized limbs, and possession by some euthycarcinoid species of sternal pores—structures possibly analogous to coxal vesicles in myriapods) contribute to uncertainty regarding their relationship to other arthropod groups; while their poor fossil record masks the evolutionary transitions within and between the separate realms they inhabited (marine, freshwater, emergent). A new euthycarcinoid from a Permian polar proglacial lake is described herein that is morphologically unlike all other euthycarcinoids, and interpreted as being well adapted for a nekton-benthic lifestyle. Antarcticarcinus pagoda n. gen. n. sp. possesses a pair of large wing-like processes that project laterally from the preabdominal dorsal exoskeleton. A trace fossil from the overlying Mackellar Formation, cf. Orbiculichnus, which was previously interpreted as having been produced by insects taking off or landing on wet sediments, is reinterpreted herein as being produced by A. pagoda n. gen. n. sp. due to the high degree of morphological similarity between traces and body fossils. This occurrence indicates that euthycarcinoids were able to adapt to life in temperate freshwater environments, while possible subaerial adaptations hint at an ability to breathe air. Indeed, if euthycarcinoids could breathe air, Cambrian terrestrial forays and rapid transition (by the Ordovician) into freshwater environments might be explained.

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Relationship between Abundance and Specific Activity of Bacterioplankton in Open Ocean Surface Waters

Applied and Environmental Microbiology ◽

10.1128/aem.02155-12 ◽

2012 ◽

Vol 79 (1) ◽

pp. 177-184 ◽

Cited By ~ 91

Author(s):

Dana E. Hunt ◽

Yajuan Lin ◽

Matthew J. Church ◽

David M. Karl ◽

Susannah G. Tringe ◽

...

Keyword(s):

Microbial Communities ◽

Specific Activity ◽

Marine Ecosystem ◽

Open Ocean ◽

Rrna Genes ◽

Cdna Libraries ◽

Content Type ◽

The Pacific ◽

Specific Activities ◽

Marine Microbial Communities

ABSTRACTMarine microbial communities are complex and dynamic, and their ecology impacts biogeochemical cycles in pelagic ecosystems. Yet, little is known about the relative activities of different microbial populations within genetically diverse communities. We used rRNA as a proxy for activity to quantify the relative specific activities (rRNA/ribosomal DNA [rDNA or rRNA genes]) of the eubacterial populations and to identify locations or clades for which there are uncouplings between specific activity and abundance. After analyzing 1.6 million sequences from 16S rDNA and rRNA (cDNA) libraries from two euphotic depths from a representative site in the Pacific Ocean, we show that although there is an overall positive relationship between the abundances (rDNAs) and activities (rRNAs) among populations of the bacterial community, for some populations these measures are uncoupled. Different ecological strategies are exemplified by the two numerically dominant clades at this site: the cyanobacteriumProchlorococcusis abundant but disproportionately more active, while the heterotrophic SAR11 is abundant but less active. Other rare populations, such asAlteromonas, have high specific activities in spite of their low abundances, suggesting intense population regulation. More detailed analyses using a complementary quantitative PCR (qPCR)-based approach of measuring relative specific activity forProchlorococcuspopulations in the Pacific and Atlantic Oceans also show that specific activity, but not abundance, reflects the key drivers of light and nutrients in this system; our results also suggest substantial top-down regulation (e.g., grazing, viruses, or organismal interactions) or transport (e.g., mixing, immigration, or emigration) of these populations. Thus, we show here that abundance and specific activity can be uncoupled in open ocean systems and that describing both is critical to characterizing microbial communities and predicting marine ecosystem functioning and responses to change.

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Sea Level, Surface Salinity of the Japan Sea, and the Younger Dryas Event in the Northwestern Pacific Ocean

Quaternary Research ◽

10.1016/0033-5894(92)90072-q ◽

1992 ◽

Vol 37 (3) ◽

pp. 346-360 ◽

Cited By ~ 91

Author(s):

L.D. Keigwin ◽

S.A. Gorbarenko

Keyword(s):

Sea Level ◽

Fresh Water ◽

Yellow River ◽

Younger Dryas ◽

Japan Sea ◽

Open Ocean ◽

Sea Surface ◽

Sea Surface Salinity ◽

Surface Salinity ◽

The Japan Sea

AbstractThe Japan Sea was profoundly different during glacial times than today. Available δ18O evidence indicates that sea surface salinity was lower by several per mil. This probably increased the stability of the water column and caused anoxic sedimentary conditions in the deep sea, as shown by the absence of benthic microfossils and the presence of laminated sediment. These changes are likely related to the effects of late Quaternary sea-level change on the shallow sills (ca. 130 m) across which the Japan Sea exchanges with the open ocean. The Hwang He (Yellow River) has previously been implicated as the source of fresh water to the Japan Sea during glaciation, but the possible roles of the Amur River and excess precipitation over evaporation must also be considered. Ambiguous radiocarbon chronologies for the latest Quaternary of Japan Sea cores do not adequately constrain the timing of salinity lowering. Previous studies have suggested that lowest sea surface salinity was achieved 27,000 to 20,000 14C yr B.P. However, if global sea-level fall restricted exchange with the open ocean circulation, then lowest salinity in the Japan Sea may have occurred as recently as 15,000 to 20,000 yr ago when sea level was lowest. If this alternative is correct, then as sea level abruptly rose about 12,000 yr ago, relatively fresh water must have been discharged to the open Pacific. This might have affected the dynamics of outflow, local faunal and floral expression of the polar front, and stable isotope ratios in foraminifera. These environmental changes could be misinterpreted as evidence for the cooling of Younger Dryas age, which has not been identified in nearby terrestrial records.

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The Azores Marine Ecosystem: An Open Window Into North Atlantic Open Ocean and Deep-Sea Environments

10.3389/978-2-88966-428-3 ◽

2021 ◽

Keyword(s):

North Atlantic ◽

Deep Sea ◽

Marine Ecosystem ◽

Open Ocean ◽

Open Window

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A state-of-the-art parameterization of atmospheric nutrient deposition fluxes in the global ocean

10.5194/egusphere-egu2020-13075 ◽

2020 ◽

Author(s):

Stelios Myriokefalitakis ◽

Matthias Gröger ◽

Jenny Hieronymus ◽

Ralf Döscher

Keyword(s):

Atmospheric Deposition ◽

State Of The Art ◽

Marine Ecosystem ◽

Open Ocean ◽

Marine Phytoplankton ◽

Global Ocean ◽

Model Calculations ◽

Deposition Fluxes ◽

Atmospheric Processing ◽

The Impact

Atmospheric deposition of trace constituents of natural and anthropogenic origin act as a nutrient source into the open ocean, affecting the marine ecosystem functioning and subsequently the exchange of CO2 between the atmosphere and the global ocean. Among other species that are deposited into the open ocean, nitrogen (N), iron (Fe), and phosphorus (P) are considered as highly significant nutrients that can limit marine phytoplankton growth and thus directly impact on ocean carbon fluxes in the ocean, particularly where the nutrient availability is the limiting factor for productivity. For this work, we take into account the up-to-date understanding of the effects of air quality on the atmospheric aerosol cycles to investigate the potential ocean biogeochemistry perturbations via the atmospheric input with the European Community Earth System Model EC-Earth (http://www.ec-earth.org/), which is jointly developed by several European institutes. In more detail, state-of-the-art N, Fe, and P atmospheric deposition fields are coupled to the embedded marine biogeochemistry model and the response of oceanic biogeochemistry to natural and anthropogenic atmospheric aerosols deposition changes is demonstrated and quantified. Model calculations show that compared to the present day, the preindustrial atmospheric deposition fluxes are calculated lower (~1.7, ~1.5, and ~1.4 times for N, Fe, and P, respectively) corresponding to a respective lower marine primary production. On the other hand, future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean (~ -15%, ~ -16% and ~ -22% for N, Fe and P, respectively) and overall to a slightly lower projected export production compared to present day. Although the impact of atmospheric processing on atmospheric inputs to the ocean results in a relatively weak response in total global-scale simulated marine productivity estimates, strong regional changes up to 40-60% are calculated in the subtropical gyres. Overall, this study indicates that both the atmospheric processing and the speciation of the atmospheric nutrients deposited in the ocean should be considered in detail in carbon-cycling studies, since they may significantly affect the marine ecosystems and thus the current estimates of the carbon cycle feedbacks to climate.This work has been financed by the National Observatory of Athens internal grant (number 5065), the &#8220;Atmospheric deposition impacts on the ocean system&#8221;, and the European Commission's Horizon 2020 Framework Programme, under Grant Agreement number 641816, the "Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination, and Outreach (CRESCENDO)".

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