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Jonathan Sharples - One of the best experts on this subject based on the ideXlab platform.
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Shelf Sea Biogeochemistry: Nutrient and carbon cycling in a temperate Shelf Sea water column
Progress in Oceanography, 2019Co-Authors: Jonathan Sharples, Daniel J. Mayor, Alex J. Poulton, Andrew P. Rees, Carol RobinsonAbstract:Abstract This special issue presents some of the key findings from the pelagic component of the UK Shelf Sea Biogeochemistry ReSearch Programme, carried out on the northwest European Shelf between March 2014 and August 2015. The project aimed to address two issues: (1) how does a temperate Shelf Sea sustain an annual net drawdown and export of atmospheric CO2 without running out of inorganic nutrients, and (2) what uncertainties in processes or parameterisations within current ecosystem models can be reduced by a coordinated, multi-disciplinary observational programme covering the full Seasonal cycle? Working with partners across Europe, the net annual drawdown of atmospheric CO2 over the entire northwest European Shelf was confirmed. This demonstrated the context and impetus for a 17-month process study in the Celtic Sea, using a long-term mooring array and several reSearch cruises, addressing Shelf Sea physics, inorganic and organic nutrient and carbon cycling, and bacterial, phytoplankton and zooplankton roles and dynamics. It was clear from the physics that all the carbon absorbed through the Sea surface over one year was not exported to the open ocean. Physical transports were too weak and too slow to transport all the carbon-laden water over a wide Shelf Sea to the Shelf edge within one year. The Shelf Sea must therefore be able to store carbon in a form that prevents release back to the atmosphere for a timescale that is sufficient to allow more episodic (timescales >1 year) exchange events to both remove the excess carbon and top-up the Shelf pool of inorganic nutrients. The results presented in this special issue illustrate the likely key role of recalcitrant dissolved organic carbon in storing carbon on the Shelf and highlight the need for longer-term measurements or monitoring to understand the nature and timing of potentially large but infrequent exchange events between the Shelf and open ocean.
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Distribution and chromatic adaptation of phytoplankton within a Shelf Sea thermocline
2015Co-Authors: Anna E. Hickman, Patrick M. Holligan, Mark C. Moore, Jonathan Sharples, Vladimir Krivtsov, Matthew R. PalmerAbstract:Observations of vertical gradients in phytoplankton community structure were made through the water column of the Seasonally stratified Celtic Sea, including within the thermocline. A deep chlorophyll maximum (DCM) was located within the thermocline at all stations, coupled to the nitracline. Vertical gradients in phytoplankton community composition were routinely observed within the thermocline. The cell abundance maxima for Synechococcus occurred in the upper part of the DCM coincident with a picoeukaryote abundance minima. Picoeukaryote abundance typically increased at or just above the peak of the DCM. Diatoms were observed occasionally at the DCM peak. Pigment compositions and phytoplankton absorption spectra indicated that the different phytoplankton communities were chromatically well adapted to the spectral composition of irradiance at the depths where they occurred in the water column. Profiles of vertical eddy diffusivity revealed that timescales for mixing between the phytoplankton layers within the thermocline were in excess of typical phytoplankton growth rates. The observed vertical gradients in community structure could therefore result from selection and niche partitioning of phytoplankton types on the light and nutrient gradient within the thermocline. The data further indicate that the pigments, light absorption characteristics, and cell size contribute to the phytoplankton selection process. The Celtic Sea, part of the temperate Northwes
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From physics to fishing over a Shelf Sea bank
Progress in Oceanography, 2013Co-Authors: Jonathan Sharples, Beth E. Scott, Mark InallAbstract:The reSearch presented in this Special Issue focuses on how Seabed topography can drive horizontal patchiness in physical and biogeochemical processes, and organism distributions in a temperate Shelf Sea during the period of established stratification in summer. The work is based upon data collected during a reSearch cruise aboard the RRS James Cook over Jones Bank in the Celtic Sea in summer 2008. Jones Bank was chosen because of its well-defined topography within an otherwise flat region of Shelf. The project arose following observations of patchiness in the chlorophyll concentration within the summer sub-surface chlorophyll maximum (SCM) of the Celtic Sea associated with marked increases in internal turbulent mixing over large bank features such as Jones Bank. These sub-surface chlorophyll patches are not apparent at the Sea surface and so cannot be detected in satellite imagery. Similar structures in sub-surface chlorophyll have been found to correlate with the distributions of foraging Seabirds in the North Sea (Scott et al., 2010). Our aim was to make measurements from the scale of turbulent microstructure, through the biogeochemical rates and phytoplankton distributions, up to the distributions of fish and Seabirds. We were motivated to determine what aspects of the Shelf system responded to the bank, and what causitive links there may be between the physical perturbation caused by the bank and the attraction of the bank for marine top predators, including fishing fleets. In this preface to the Special Issue we will describe the physical and biological environment of the Celtic Sea, using earlier data to highlight the likely effects of a bank on Shelf Sea structure, and set the context and pose the questions addressed by the papers in this issue. We then summarise the findings of the reSearch, and provide a synthesis describing why banks in a stratified Shelf Sea may attract mobile marine predators.
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Enhanced nutrient fluxes at the Shelf Sea Seasonal thermocline caused by stratified flow over a bank
Progress in Oceanography, 2013Co-Authors: Jacqueline F. Tweddle, Jonathan Sharples, Matthew R. Palmer, Keith Davidson, Sharon McneillAbstract:Patches of enhanced chlorophyll a (Chl) concentrations within the thermocline were observed over the slopes of several banks in the Celtic Sea. The turbulent mixing of nutrients from the bottom water into the thermocline was found to be greatly enhanced over the slope of a bank (up to 52 mmol nitrate m−2 day−1), compared to over nearby flat Seafloor (∼2 mmol nitrate m−2 day−1). This increased nutrient supply, forced by locally generated lee waves and internal mixing, is greater than nitrate supplies to the productive tidal mixing fronts or to the Shelf edge. We hypothesize this nutrient flux promotes an increase in phytoplankton growth in the thermocline over and downstream of Shelf Sea banks, contributing to the horizontal patchiness in the thermocline Chl signal. The persistence of the strong biological response to mixing at the bank, combined with the ubiquity of Shelf Sea banks, suggests these bathymetric features have wide importance for “new” primary production in Shelf Seas.
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Impacts of climate change on Shelf Sea stratification
2013Co-Authors: Jonathan Sharples, Jason Holt, Stephen DyeAbstract:Temperature stratification over the NW European Shelf Seas is showing evidence of beginning slightly earlier in the year, on average. There is some suggestion of strengthening of stratification beyond the normal inter-annual variability. Trends in stratification in regions influenced by fresh water inputs are also not apparent against the background of natural variability. Predictions for the end of this century suggest that thermal stratification will begin typically 1 week earlier than at present, and end 5 – 10 days later. The strength of the stratification over the whole NW European Shelf Seas is projected to increase in response to changes in the Seasonal heating cycle. Changes to coastal stratification caused by inputs of fresh water cannot yet be predicted.
Silke Voigt - One of the best experts on this subject based on the ideXlab platform.
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campanian maastrichtian carbon isotope stratigraphy Shelf ocean correlation between the european Shelf Sea and the tropical pacific ocean
Newsletters on Stratigraphy, 2010Co-Authors: Silke Voigt, Oliver Friedrich, Richard D Norris, Joachim SchonfeldAbstract:The long-term climate cooling during Campanian - Maastrichtian times is not well understood to date, especially because of the uncertainty introduced by low temporal resolution of biostratigraphy and the pronounced provincialism between tropical and temperate taxa. Two new high-resolution carbon isotope records derived from the boreal Shelf-Sea section at Lagerdorf-Kronsmoor-Hemmoor, northern Germany and the tropical Pacific at Deep Sea Drilling Project Site 305, Shatsky Rise, reduce these uncertainties. The records can be correlated with an accuracy not achieved by biostratigraphic methods so far. Distinct carbon isotope events in the late Campanian and the early Maastrichtian can be identified at both localities suggesting to represent global carbon cycle perturbations. Especially, the negative carbon isotope excursion in the early Maastrichtian, a pronounced feature of open-ocean records from the Pacific and Southern oceans, is recognized for the first time at a Shelf-Sea locality related to the North Atlantic Ocean. Furthermore, two short-term positive excursions are identified as superimposed signals to this event. The improved stratigraphy provides the unique opportunity to recognize leads and lags between the carbon cycle and ocean circulation of different marine settings and ecosystems, leading to a better understanding of their causes and effects.
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Midlatitude Shelf Seas in the Cenomanian‐Turonian greenhouse world: Temperature evolution and North Atlantic circulation
Paleoceanography, 2004Co-Authors: Silke Voigt, Andrew S Gale, Sascha FlogelAbstract:[1] An 8 million year record of subtropical and midlatitude Shelf-Sea temperatures, derived from oxygen isotopes of well-preserved brachiopods from a variety of European sections, demonstrates a long-term Cenomanian temperature rise (16–20°C, midlatitudes) that reached its maximum early in the late Turonian (23°C, midlatitudes). Superimposed on the long-term trend, Shelf-Sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations. In the mid-Cenomanian and the late Turonian, two minor Shelf-Sea cooling events (2–3°C) coincide with carbon cycle perturbations and times of high-amplitude Sea level falls. Although this evidence supports the hypothesis of potential glacioeustatic effects on Cretaceous Sea level, the occurrence of minimum Shelf-Sea temperatures within transgressive beds argues for regional changes in Shelf-Sea circulation as the most plausible mechanism. The major carbon cycle event in the latest Cenomanian (oceanic anoxic event 2) is accompanied by a substantial increase in Shelf-Sea temperatures (4–5°C) that occurred ∼150 kyr after the commencement of the δ13C excursion and is related to the spread of oceanic conditions in western European Shelf-Sea basins. Our oxygen isotope record and published δ18O data of pristinely preserved foraminifera allow the consideration of North Atlantic surface water properties in the Cenomanian along a transect from the tropics to the midlatitudes. On the basis of fossil-derived δ18O, estimated δw ranges, and modeled salinities, temperature-salinity-density ranges were estimated for tropical, subtropical, and midlatitude surface waters. Accordingly, the Cenomanian temperate Shelf-Seas waters have potentially the highest surface water density and could have contributed to North Atlantic intermediate to deep waters in the preopening stage of the equatorial Atlantic gateway.
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midlatitude Shelf Seas in the cenomanian turonian greenhouse world temperature evolution and north atlantic circulation
Paleoceanography, 2004Co-Authors: Silke Voigt, Andrew S Gale, Sascha FlogelAbstract:[1] An 8 million year record of subtropical and midlatitude Shelf-Sea temperatures, derived from oxygen isotopes of well-preserved brachiopods from a variety of European sections, demonstrates a long-term Cenomanian temperature rise (16–20°C, midlatitudes) that reached its maximum early in the late Turonian (23°C, midlatitudes). Superimposed on the long-term trend, Shelf-Sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations. In the mid-Cenomanian and the late Turonian, two minor Shelf-Sea cooling events (2–3°C) coincide with carbon cycle perturbations and times of high-amplitude Sea level falls. Although this evidence supports the hypothesis of potential glacioeustatic effects on Cretaceous Sea level, the occurrence of minimum Shelf-Sea temperatures within transgressive beds argues for regional changes in Shelf-Sea circulation as the most plausible mechanism. The major carbon cycle event in the latest Cenomanian (oceanic anoxic event 2) is accompanied by a substantial increase in Shelf-Sea temperatures (4–5°C) that occurred ∼150 kyr after the commencement of the δ13C excursion and is related to the spread of oceanic conditions in western European Shelf-Sea basins. Our oxygen isotope record and published δ18O data of pristinely preserved foraminifera allow the consideration of North Atlantic surface water properties in the Cenomanian along a transect from the tropics to the midlatitudes. On the basis of fossil-derived δ18O, estimated δw ranges, and modeled salinities, temperature-salinity-density ranges were estimated for tropical, subtropical, and midlatitude surface waters. Accordingly, the Cenomanian temperate Shelf-Seas waters have potentially the highest surface water density and could have contributed to North Atlantic intermediate to deep waters in the preopening stage of the equatorial Atlantic gateway.
Sascha Flogel - One of the best experts on this subject based on the ideXlab platform.
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Midlatitude Shelf Seas in the Cenomanian‐Turonian greenhouse world: Temperature evolution and North Atlantic circulation
Paleoceanography, 2004Co-Authors: Silke Voigt, Andrew S Gale, Sascha FlogelAbstract:[1] An 8 million year record of subtropical and midlatitude Shelf-Sea temperatures, derived from oxygen isotopes of well-preserved brachiopods from a variety of European sections, demonstrates a long-term Cenomanian temperature rise (16–20°C, midlatitudes) that reached its maximum early in the late Turonian (23°C, midlatitudes). Superimposed on the long-term trend, Shelf-Sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations. In the mid-Cenomanian and the late Turonian, two minor Shelf-Sea cooling events (2–3°C) coincide with carbon cycle perturbations and times of high-amplitude Sea level falls. Although this evidence supports the hypothesis of potential glacioeustatic effects on Cretaceous Sea level, the occurrence of minimum Shelf-Sea temperatures within transgressive beds argues for regional changes in Shelf-Sea circulation as the most plausible mechanism. The major carbon cycle event in the latest Cenomanian (oceanic anoxic event 2) is accompanied by a substantial increase in Shelf-Sea temperatures (4–5°C) that occurred ∼150 kyr after the commencement of the δ13C excursion and is related to the spread of oceanic conditions in western European Shelf-Sea basins. Our oxygen isotope record and published δ18O data of pristinely preserved foraminifera allow the consideration of North Atlantic surface water properties in the Cenomanian along a transect from the tropics to the midlatitudes. On the basis of fossil-derived δ18O, estimated δw ranges, and modeled salinities, temperature-salinity-density ranges were estimated for tropical, subtropical, and midlatitude surface waters. Accordingly, the Cenomanian temperate Shelf-Seas waters have potentially the highest surface water density and could have contributed to North Atlantic intermediate to deep waters in the preopening stage of the equatorial Atlantic gateway.
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midlatitude Shelf Seas in the cenomanian turonian greenhouse world temperature evolution and north atlantic circulation
Paleoceanography, 2004Co-Authors: Silke Voigt, Andrew S Gale, Sascha FlogelAbstract:[1] An 8 million year record of subtropical and midlatitude Shelf-Sea temperatures, derived from oxygen isotopes of well-preserved brachiopods from a variety of European sections, demonstrates a long-term Cenomanian temperature rise (16–20°C, midlatitudes) that reached its maximum early in the late Turonian (23°C, midlatitudes). Superimposed on the long-term trend, Shelf-Sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations. In the mid-Cenomanian and the late Turonian, two minor Shelf-Sea cooling events (2–3°C) coincide with carbon cycle perturbations and times of high-amplitude Sea level falls. Although this evidence supports the hypothesis of potential glacioeustatic effects on Cretaceous Sea level, the occurrence of minimum Shelf-Sea temperatures within transgressive beds argues for regional changes in Shelf-Sea circulation as the most plausible mechanism. The major carbon cycle event in the latest Cenomanian (oceanic anoxic event 2) is accompanied by a substantial increase in Shelf-Sea temperatures (4–5°C) that occurred ∼150 kyr after the commencement of the δ13C excursion and is related to the spread of oceanic conditions in western European Shelf-Sea basins. Our oxygen isotope record and published δ18O data of pristinely preserved foraminifera allow the consideration of North Atlantic surface water properties in the Cenomanian along a transect from the tropics to the midlatitudes. On the basis of fossil-derived δ18O, estimated δw ranges, and modeled salinities, temperature-salinity-density ranges were estimated for tropical, subtropical, and midlatitude surface waters. Accordingly, the Cenomanian temperate Shelf-Seas waters have potentially the highest surface water density and could have contributed to North Atlantic intermediate to deep waters in the preopening stage of the equatorial Atlantic gateway.
Andrew S Gale - One of the best experts on this subject based on the ideXlab platform.
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changing ocean circulation and hydrothermal inputs during ocean anoxic event 2 cenomanian turonian evidence from nd isotopes in the european Shelf Sea
Earth and Planetary Science Letters, 2013Co-Authors: Xinyuan Zheng, Hugh C Jenkyns, Andrew S Gale, David Ward, Gideon M HendersonAbstract:Nd isotopes of fish debris collected from the English Chalk at Eastbourne (Sussex, UK) are used to reconstruct the history of ocean circulation in the NW European Shelf Sea during Oceanic Anoxic Event 2 (OAE 2, Cenomanian–Turonian). The Eastbourne eNd record exhibits a 1-unit negative excursion (decreasing from ∼−9 to ∼−10), immediately followed by a 3-unit positive excursion reaching ∼−7. The onset of the negative eNd excursion lags the global δ13C rise characteristic of OAE 2, suggesting stable patterns of ocean circulation in the NW European Shelf Sea at this time. Both negative and positive Nd-isotope excursions took place during a transient cooling episode within OAE 2. The negative eNd excursion is interpreted as due to a change in ocean circulation with northerly sourced water masses becoming the dominant bottom waters at Eastbourne. The positive excursion is best explained by the transport of radiogenic Nd derived from a volcanic source, possibly the High Arctic or Caribbean large igneous province (LIP). An input of volcanic Nd may reconcile the Eastbourne record with coeval eNd records on Demerara Rise in the western tropical Atlantic. The broad synchroneity of high eNd values (∼−7) registered at both sites suggests a possible period with efficient oceanic mixing between the tropical Atlantic and the NW European Shelf Sea during the cooling episode. The Eastbourne eNd record of OAE 2, together with coeval temperature reconstructions, provides evidence for the coincidence of changes in ocean circulation and transient climatic cooling, implying a tight coupling between the two phenomena during this interval.
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Midlatitude Shelf Seas in the Cenomanian‐Turonian greenhouse world: Temperature evolution and North Atlantic circulation
Paleoceanography, 2004Co-Authors: Silke Voigt, Andrew S Gale, Sascha FlogelAbstract:[1] An 8 million year record of subtropical and midlatitude Shelf-Sea temperatures, derived from oxygen isotopes of well-preserved brachiopods from a variety of European sections, demonstrates a long-term Cenomanian temperature rise (16–20°C, midlatitudes) that reached its maximum early in the late Turonian (23°C, midlatitudes). Superimposed on the long-term trend, Shelf-Sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations. In the mid-Cenomanian and the late Turonian, two minor Shelf-Sea cooling events (2–3°C) coincide with carbon cycle perturbations and times of high-amplitude Sea level falls. Although this evidence supports the hypothesis of potential glacioeustatic effects on Cretaceous Sea level, the occurrence of minimum Shelf-Sea temperatures within transgressive beds argues for regional changes in Shelf-Sea circulation as the most plausible mechanism. The major carbon cycle event in the latest Cenomanian (oceanic anoxic event 2) is accompanied by a substantial increase in Shelf-Sea temperatures (4–5°C) that occurred ∼150 kyr after the commencement of the δ13C excursion and is related to the spread of oceanic conditions in western European Shelf-Sea basins. Our oxygen isotope record and published δ18O data of pristinely preserved foraminifera allow the consideration of North Atlantic surface water properties in the Cenomanian along a transect from the tropics to the midlatitudes. On the basis of fossil-derived δ18O, estimated δw ranges, and modeled salinities, temperature-salinity-density ranges were estimated for tropical, subtropical, and midlatitude surface waters. Accordingly, the Cenomanian temperate Shelf-Seas waters have potentially the highest surface water density and could have contributed to North Atlantic intermediate to deep waters in the preopening stage of the equatorial Atlantic gateway.
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midlatitude Shelf Seas in the cenomanian turonian greenhouse world temperature evolution and north atlantic circulation
Paleoceanography, 2004Co-Authors: Silke Voigt, Andrew S Gale, Sascha FlogelAbstract:[1] An 8 million year record of subtropical and midlatitude Shelf-Sea temperatures, derived from oxygen isotopes of well-preserved brachiopods from a variety of European sections, demonstrates a long-term Cenomanian temperature rise (16–20°C, midlatitudes) that reached its maximum early in the late Turonian (23°C, midlatitudes). Superimposed on the long-term trend, Shelf-Sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations. In the mid-Cenomanian and the late Turonian, two minor Shelf-Sea cooling events (2–3°C) coincide with carbon cycle perturbations and times of high-amplitude Sea level falls. Although this evidence supports the hypothesis of potential glacioeustatic effects on Cretaceous Sea level, the occurrence of minimum Shelf-Sea temperatures within transgressive beds argues for regional changes in Shelf-Sea circulation as the most plausible mechanism. The major carbon cycle event in the latest Cenomanian (oceanic anoxic event 2) is accompanied by a substantial increase in Shelf-Sea temperatures (4–5°C) that occurred ∼150 kyr after the commencement of the δ13C excursion and is related to the spread of oceanic conditions in western European Shelf-Sea basins. Our oxygen isotope record and published δ18O data of pristinely preserved foraminifera allow the consideration of North Atlantic surface water properties in the Cenomanian along a transect from the tropics to the midlatitudes. On the basis of fossil-derived δ18O, estimated δw ranges, and modeled salinities, temperature-salinity-density ranges were estimated for tropical, subtropical, and midlatitude surface waters. Accordingly, the Cenomanian temperate Shelf-Seas waters have potentially the highest surface water density and could have contributed to North Atlantic intermediate to deep waters in the preopening stage of the equatorial Atlantic gateway.
Matthew R. Palmer - One of the best experts on this subject based on the ideXlab platform.
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AlterEco: An Alternative Framework to Assess Marine Ecosystem Functioning in Shelf Seas
2020Co-Authors: Matthew R. Palmer, Charlotte Williams, Anil Akpinar, Claire Mahaffey, Tom Hull, Matthew TobermanAbstract:<p>A recognized global increase in the extent of Shelf Sea and coastal oxygen deficiency calls for an urgent need to increase the spatial and temporal measurement of oxygen and a better understanding of the processes that lead to oxygen deficiency. This need is severely impeded by the natural complexity of ecosystem functioning, the impact of a changing climate, connectivity between different regions of our Shelf Seas and large-scale external forcing from ocean and atmosphere. Currently, methods are severely restricted in resolving this complexity due to poor resolution in observational coverage, which calls for the development of new strategies for observing and monitoring marine ecosystem and environmental status to better enable national and regional assessments.</p><p>AlterEco is a UK based project that has been jointly funded by academic and government agencies and the WWF to address this challenge using a novel monitoring framework to deliver improved understanding of key Shelf Sea ecosystem drivers. This framework capitalizes on recent UK investments in marine autonomous vehicles, such as ocean gliders and wave-driven surface vehicles, and state-of-the-art chemical sensors to investigate the physical and biogeochemical functioning in the North Sea from autumn 2017 to spring 2019. The chosen area is known to undergo variable physical, chemical and biological conditioning and includes areas previously identified to experience Seasonal bottom layer oxygen depletion. We will present analysis of the effectiveness of the chosen framework to meet assessments of good environmental status and will discuss the global transferability of this approach.</p>
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Distribution and chromatic adaptation of phytoplankton within a Shelf Sea thermocline
2015Co-Authors: Anna E. Hickman, Patrick M. Holligan, Mark C. Moore, Jonathan Sharples, Vladimir Krivtsov, Matthew R. PalmerAbstract:Observations of vertical gradients in phytoplankton community structure were made through the water column of the Seasonally stratified Celtic Sea, including within the thermocline. A deep chlorophyll maximum (DCM) was located within the thermocline at all stations, coupled to the nitracline. Vertical gradients in phytoplankton community composition were routinely observed within the thermocline. The cell abundance maxima for Synechococcus occurred in the upper part of the DCM coincident with a picoeukaryote abundance minima. Picoeukaryote abundance typically increased at or just above the peak of the DCM. Diatoms were observed occasionally at the DCM peak. Pigment compositions and phytoplankton absorption spectra indicated that the different phytoplankton communities were chromatically well adapted to the spectral composition of irradiance at the depths where they occurred in the water column. Profiles of vertical eddy diffusivity revealed that timescales for mixing between the phytoplankton layers within the thermocline were in excess of typical phytoplankton growth rates. The observed vertical gradients in community structure could therefore result from selection and niche partitioning of phytoplankton types on the light and nutrient gradient within the thermocline. The data further indicate that the pigments, light absorption characteristics, and cell size contribute to the phytoplankton selection process. The Celtic Sea, part of the temperate Northwes
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Enhanced nutrient fluxes at the Shelf Sea Seasonal thermocline caused by stratified flow over a bank
Progress in Oceanography, 2013Co-Authors: Jacqueline F. Tweddle, Jonathan Sharples, Matthew R. Palmer, Keith Davidson, Sharon McneillAbstract:Patches of enhanced chlorophyll a (Chl) concentrations within the thermocline were observed over the slopes of several banks in the Celtic Sea. The turbulent mixing of nutrients from the bottom water into the thermocline was found to be greatly enhanced over the slope of a bank (up to 52 mmol nitrate m−2 day−1), compared to over nearby flat Seafloor (∼2 mmol nitrate m−2 day−1). This increased nutrient supply, forced by locally generated lee waves and internal mixing, is greater than nitrate supplies to the productive tidal mixing fronts or to the Shelf edge. We hypothesize this nutrient flux promotes an increase in phytoplankton growth in the thermocline over and downstream of Shelf Sea banks, contributing to the horizontal patchiness in the thermocline Chl signal. The persistence of the strong biological response to mixing at the bank, combined with the ubiquity of Shelf Sea banks, suggests these bathymetric features have wide importance for “new” primary production in Shelf Seas.
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internal tide coherence and decay over a wide Shelf Sea
Geophysical Research Letters, 2011Co-Authors: Mark Inall, Jonathan Sharples, Matthew R. Palmer, Dimitry Aleynik, Tim BoydAbstract:[1] A quasi-synoptic hydrography and velocity section is used to determine the structure and the decay rate of the internal tide (IT) across the broad continental Shelf of the Celtic Sea. In these observations the IT is coherent over more than 170 km, about five wavelengths, with an estimated shoreward energy decay scale of 42 km. The inferred IT wavelength-averaged dissipation rate near the Shelf edge is estimated as 2.08 × 10−7 Wkg−1, in close agreement with tidally- and vertically-averaged measurements from the region. These results provide the firstin situ evidence of IT coherence over many wavelengths in a Shelf Sea.
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An investigation of internal mixing in a Seasonally stratified Shelf Sea
Journal of Geophysical Research: Oceans, 2008Co-Authors: Matthew R. Palmer, Tom P. Rippeth, John H. SimpsonAbstract:The Shelf Sea Seasonal thermocline is a critical interface within the marine environment, separating the euphotic zone from nutrient-rich deep water. Fluxes across the thermocline therefore represent a key biogeochemical pathway. In this paper we quantify the rate of mixing across the Seasonal thermocline for a location in the Celtic Sea and investigate the processes responsible for driving thermocline fluxes. Profiles of the rate of dissipation of turbulent kinetic energy (e) show enhanced dissipation within the thermocline region (similar to 6 x 10(-5) W m(-3)). The diffusivity implied by these measurements is similar to 0.5 cm(2) s(-1), similar to previous Shelf Sea studies, and is sufficient to explain the observed warming of the deep water, suggesting that vertical mixing is the dominant control on water column structure. Two potential sources of mixing energy are identified, the internal tide and near-inertial waves. The mechanism of energy transfer from the candidate ! mixing mechanisms to turbulence is not clear. Thermocline dissipation rates were found to have no Richardson number dependence, but scaled positively with N-2 and S-2, in agreement with a previous turbulence parameterization. Application of this model to our data does a good job of capturing the mean characteristics of the observed heating flux across the thermocline, although none of the short-term fluctuations in mixing were reproduced