Physical preconditioning of oxygen depletion in shelf seas

The global ocean dissolved oxygen (DO) inventory is decreasing and the areal extent of DO deficiency is increasing. In the shelf sea BML, net DO removal can occur as a result of restricted ventilation due to seasonal thermal stratification, oxygen consumption via pelagic and benthic respiration of organic matter, and nitrification. DO decline is becoming evident in several shelf seas, with recent model studies estimating that large regions of the Northwest European continental shelf seas (325,000 to 400,000 km2) have the potential to become seasonally deficient in DO in late summer. It is therefore of vital importance that DO is monitored accurately and effectively in shelf seas.Here we present results from AlterECO project, which aimed to provide an alternative, novel framework for the monitoring of shelf sea ecosystem health indicators, including DO, via the deployment of 20 gliders in the North Sea (NW European shelf). Between November 2017 and May 2019 the gliders provided 18 month continuous measurements of T, S, chlorophyll fluorescence, and DO in the seasonally stratified study area, capturing the onset and breakdown of two spring blooms. In both years the gliders captured a weakly stratified, deep (>60m) thermocline in late autumn which was responsible for oxygen deplete (75%)&#160; &#8216;pools&#8217; in the North Sea. Our results show that preconditioning of pre-bloom transitional periods as well as episodic mixing events drive inter-annual differences in BML DO concentrations. Large inter-annual variability between pre-bloom physical conditions was observed, with the occurrence of anticyclone Hartmut in February 2018 resulting in a much colder water column (and therefore higher solubility of DO) in spring 2018 than 2019. Additionally we will demonstrate that the erosion of mini-blooms during the onset of stratification results in mixing of supersaturated DO surface water into the BML, helping to prevent DO deficiency in the BML in late summer. Comparisons of our high resolution glider data with the latest state of the art biogeochemical models (AMM15-ERSEM) will also be presented. We postulate that understanding the drivers of inter-annual variability in pre-bloom physical conditions is crucial in terms of understanding and predicting DO depletion in shelf seas.&#160;

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A satellite-based Lagrangian view on the origin of water-masses in the northern European shelf seas

10.5194/egusphere-egu21-2220 ◽

2021 ◽

Author(s):

Ezra Eisbrenner ◽

Léon Chafik

Keyword(s):

North Sea ◽

Water Mass ◽

Sea Water ◽

Water Masses ◽

Subpolar Gyre ◽

The North ◽

Shelf Seas ◽

Shelf Sea ◽

The North Sea ◽

Northern North Sea

Knowledge about water-mass properties is critical to understanding how ocean climate variability impacts the shelf seas. Disentangling the origin of shelf sea water-masses and associated driving mechanisms is, therefore, a significant step towards improving the predictive skill related to water-mass evolution. Especially more conservative water-mass properties, even of surface waters, have the potential to reveal links between the shelf seas and large-scale ocean circulation regimes when traced back to their origin. The northern North Sea for example as the main gateway for water-masses to one of Europe's largest shelf sea areas is largely supplied by water-masses from the open North Atlantic, a connection which can be seen from, e.g., sea surface salinity.The aim of this study is to identify the origin of northern North Sea water-masses and distinguish pathway variability relative to the subpolar gyre regimes. This is done using Lagrangian trajectories, calculated using satellite-derived velocity fields. The results of the Lagrangian statistics mainly indicate that on inter-annual time-scales the North Atlantic subpolar gyre strength largely influences the water-masses found in the North Sea. The relation is found to originate from varying pathways and therefore origin. We conclude that on inter-annual time scales the subpolar gyre strength is a good proxy and skillful predictor of water-mass variability in the North Sea.

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Introduction to the North Sea Project

Philosophical Transactions of the Royal Society of London Series A Physical and Engineering Sciences ◽

10.1098/rsta.1993.0053 ◽

1993 ◽

Vol 343 (1669) ◽

pp. 379-382 ◽

Cited By ~ 1

Keyword(s):

North Sea ◽

Royal Society ◽

Economic Importance ◽

The North ◽

The Future ◽

Shelf Seas ◽

Shelf Sea ◽

The North Sea ◽

Heavy Burden ◽

Intellectual Challenge

It is more than ten years since the Royal Society last hosted a discussion to focus on the Shelf Seas. The intervening period has been a time of both exciting scientific developments and an emerging awareness of the practical and economic importance of our shallow coastal seas. Concern about the welfare of the environment in these waters, on which we place an increasingly heavy burden, has added to the intellectual challenge of understanding the processes that control that environment and lent impetus to the development of improved models of the shelf sea system which will be needed for informed management in the future as pressures from our agriculture and industry increase.

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Quantifying the impact of the major driving mechanisms of inter-annual variability of salinity in the North Sea

Progress In Oceanography ◽

10.1016/j.pocean.2017.04.004 ◽

2017 ◽

Vol 154 ◽

pp. 25-37 ◽

Cited By ~ 2

Author(s):

Ismael Núñez-Riboni ◽

Anna Akimova

Keyword(s):

North Sea ◽

Annual Variability ◽

The North ◽

Driving Mechanisms ◽

The North Sea ◽

The Impact

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Metabarcoding reveals different zooplankton communities in northern and southern areas of the North Sea

10.1101/2020.07.23.218479 ◽

2020 ◽

Author(s):

Jan Niklas Macher ◽

Berry B. van der Hoorn ◽

Katja T. C. A. Peijnenburg ◽

Lodewijk van Walraven ◽

Willem Renema

Keyword(s):

North Sea ◽

Zooplankton Community ◽

Taxonomic Diversity ◽

Molecular Techniques ◽

Trophic Levels ◽

List Type ◽

The North ◽

Shelf Sea ◽

The North Sea ◽

Zooplankton Communities

AbstractZooplankton are key players in marine ecosystems, linking primary production to higher trophic levels. The high abundance and high taxonomic diversity renders zooplankton ideal for biodiversity monitoring. However, taxonomic identification of the zooplankton assemblage is challenging due to its high diversity, subtle morphological differences and the presence of many meroplanktonic species, especially in coastal seas. Molecular techniques such as metabarcoding can help with rapid processing and identification of taxa in complex samples, and are therefore promising tools for identifying zooplankton communities. In this study, we applied metabarcoding of the mitochondrial cytochrome c oxidase I gene to zooplankton samples collected along a latitudinal transect in the North Sea, a shelf sea of the Atlantic Ocean. Northern regions of the North Sea are influenced by inflow of oceanic Atlantic waters, whereas the southern parts are characterised by more coastal waters. Our metabarcoding results indicated strong differences in zooplankton community composition between northern and southern areas of the North Sea, particularly in the classes Copepoda, Actinopterygii (ray-finned fishes) and Polychaeta. We compared these results to the known distributions of species reported in previous studies, and by comparing the abundance of copepods to data obtained from the Continuous Plankton Recorder (CPR). We found that our metabarcoding results are mostly congruent with the reported distribution and abundance patterns of zooplankton species in the North Sea. Our results highlight the power of metabarcoding to rapidly assess complex zooplankton samples, and we suggest that the technique could be used in future monitoring campaigns and biodiversity assessments.HighlightsZooplankton communities are different in northern and southern areas of the North SeaMetabarcoding results are consistent with known species distributions and abundanceMetabarcoding allows for fast identification of meroplanktonic species

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The effects of climate change on persistent organic pollutants (POPs) in the North Sea

Ocean Science Discussions ◽

10.5194/osd-10-1525-2013 ◽

2013 ◽

Vol 10 (5) ◽

pp. 1525-1557

Author(s):

K. O'Driscoll ◽

B. Mayer ◽

J. Su ◽

M. Mathis

Keyword(s):

Climate Change ◽

Organic Pollutants ◽

North Sea ◽

21St Century ◽

Persistent Organic Pollutants ◽

Global Ocean ◽

Open Boundary ◽

The North ◽

The Future ◽

The North Sea

Abstract. The fate and cycling of two selected legacy persistent organic pollutants (POPs), PCB 153 and γ-HCH, in the North Sea in the 21st century have been modelled with combined hydrodynamic and fate and transport ocean models. To investigate the impact of climate variability on POPs in the North Sea in the 21st century, future scenario model runs for three 10 yr periods to the year 2100 using plausible levels of both in situ concentrations and atmospheric, river and open boundary inputs are performed. Since estimates of future concentration levels of POPs in the atmosphere, oceans and rivers are not available, our approach was to reutilise 2005 values in the atmosphere, rivers and at the open ocean boundaries for every year of the simulations. In this way, we attribute differences between the three 10 yr simulations to climate change only. For the HAMSOM and atmospheric forcing, results of the IPCC A1B (SRES) 21st century scenario are utilised, where surface forcing is provided by the REMO downscaling of the ECHAM5 global atmospheric model, and open boundary conditions are provided by the MPIOM global ocean model. Dry gas deposition and volatilisation of γ-HCH increase in the future relative to the present. In the water column, total mass of γ-HCH and PCB 153 remain fairly steady in all three runs. In sediment, γ-HCH increases in the future runs, relative to the present, while PCB 153 in sediment decreases exponentially in all three runs, but even faster in the future, both of which are the result of climate change. Annual net sinks exceed sources at the ends of all periods.

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Depth-averaged instantaneous currents in a tidally dominated shelf sea from glider observations

10.5194/bg-2016-118 ◽

2016 ◽

Author(s):

Lucas Merckelbach

Keyword(s):

Real Time ◽

North Sea ◽

Current Data ◽

Pass Filter ◽

Low Pass Filter ◽

Real Time Mode ◽

The North ◽

Shelf Sea ◽

The North Sea ◽

Better Than

Abstract. Ocean gliders have become ubiquitous observation platforms in the ocean in recent years. They are also increasingly used in coastal environments. The coastal observatory system COSYNA has pioneered the use of gliders in the North Sea, a shallow tidally energetic shelf sea. For operational reasons, the gliders operated in the North Sea are programmed to resurface every 3–5 hours. The glider's deadreckoning algorithm yields depth averaged currents, averaged in time over each subsurface interval. Under operational conditions these averaged currents are a poor approximation of the instantaneous tidal current. In this work an algorithm is developed that estimates the instantaneous current (tidal and residual) from glider observations only. The algorithm uses a second-order Butterworth low-pass filter to estimate the residual current component, and a Kalman filter based on the linear shallow water equations for the tidal component. A comparison of data from a glider experiment with current data from an ADCP deployed nearby shows that the standard deviations for the east and north current components are better than 7 cm s−1 in near-real time mode, and improve to better than 5 cm s−1 in delayed mode, where the filters can be run forward and backward. In the near-real time mode the algorithm provides estimates of the currents that the glider is expected to encounter during its next few dives. Combined with a behavioural and dynamic model of the glider, this yields predicted trajectories, the information of which is incorporated in warning messages issued to ships by the (German) authorities. In delayed mode the algorithm produces useful estimates of the depth averaged currents, which can be used in (process-based) analyses in case no other source of measured current information is available.

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Recent Coccolith Sedimentation Patterns and Transport in the North Sea: Implications for Palaeoceanographic Studies of Marginal and Continental Shelf Seas

Applied Micropalaeontology ◽

10.1007/978-94-017-0763-3_1 ◽

1993 ◽

pp. 1-39 ◽

Cited By ~ 3

Author(s):

Simon D. Houghton

Keyword(s):

Continental Shelf ◽

North Sea ◽

The North ◽

Shelf Seas ◽

The North Sea

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Depth-averaged instantaneous currents in a tidally dominated shelf sea from glider observations

Biogeosciences ◽

10.5194/bg-13-6637-2016 ◽

2016 ◽

Vol 13 (24) ◽

pp. 6637-6649 ◽

Cited By ~ 1

Author(s):

Lucas Merckelbach

Keyword(s):

Real Time ◽

North Sea ◽

Current Data ◽

Pass Filter ◽

Low Pass Filter ◽

Real Time Mode ◽

The North ◽

Shelf Sea ◽

The North Sea ◽

Better Than

Abstract. Ocean gliders have become ubiquitous observation platforms in the ocean in recent years. They are also increasingly used in coastal environments. The coastal observatory system COSYNA has pioneered the use of gliders in the North Sea, a shallow tidally energetic shelf sea. For operational reasons, the gliders operated in the North Sea are programmed to resurface every 3–5 h. The glider's dead-reckoning algorithm yields depth-averaged currents, averaged in time over each subsurface interval. Under operational conditions these averaged currents are a poor approximation of the instantaneous tidal current. In this work an algorithm is developed that estimates the instantaneous current (tidal and residual) from glider observations only. The algorithm uses a first-order Butterworth low pass filter to estimate the residual current component, and a Kalman filter based on the linear shallow water equations for the tidal component. A comparison of data from a glider experiment with current data from an acoustic Doppler current profilers deployed nearby shows that the standard deviations for the east and north current components are better than 7 cm s−1 in near-real-time mode and improve to better than 6 cm s−1 in delayed mode, where the filters can be run forward and backward. In the near-real-time mode the algorithm provides estimates of the currents that the glider is expected to encounter during its next few dives. Combined with a behavioural and dynamic model of the glider, this yields predicted trajectories, the information of which is incorporated in warning messages issued to ships by the (German) authorities. In delayed mode the algorithm produces useful estimates of the depth-averaged currents, which can be used in (process-based) analyses in case no other source of measured current information is available.

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