Bathymetric Properties of the Baltic Sea

Stranne, Christian; O’Regan, Matt; Greenwood, Sarah L.; Gustafsson, Bo; Humborg, Christoph; Weidner, Elizabeth

doi:10.5194/os-2019-18

Cited by 3 publications

(4 citation statements)

References 38 publications

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“…(2020) and also in the high‐resolution multibeam data from R/V Electra presented in Jakobsson et al. (2019).…”

Section: Discussionmentioning

confidence: 82%

“…Jakobsson et al. (2019) provide a detailed comparison of the Åland Sea bottom topography in high‐resolution multibeam data from the R/V Electra and two digital bathymetric models (DBMs): IOWTOPO (resolution of 2 × 1 arcmin, Seifert et al., 2001) and the more recent EMODnet (resolution of 1/16 × 1/16 arcmin, EMODnet Bathymetry Consortium, 2018). While the main morphology of the Åland Sea is well represented in EMODnet compared to the high‐resolution data from R/V Electra , the coarser resolved IOWTOPO DBM, on which our model bathymetry is based, only gives a rough picture of the highly complex Åland Sea bottom topography.…”

Section: Discussionmentioning

confidence: 99%

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Revisiting the Role of Convective Deep Water Formation in Northern Baltic Sea Bottom Water Renewal

et al. 2020

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Deep water renewal and ventilation of the Baltic Sea is commonly considered to occur solely via saltwater inflows from the North Sea. However, recent analysis of geophysical and sediment proxy data suggests convective deep water formation during wintertime as a second process that has contributed to the ventilation of the northern and central Baltic Sea bottom waters during cold climate periods. Here, we investigate the role of deep water formation in the northern Baltic Sea in a regional ocean circulation model. Selecting the particularly cold winter 1986/1987 as a reference period, we perform sensitivity experiments in which the atmospheric temperature forcing is changed and/or localized brine rejection on subgrid scales is accounted for through a parameterization. We study the sinking and circulation of water masses via passive tracers introduced into the model. Generally, our model results support the established view that convective deep water formation does not play a major role in Baltic Sea deep water renewal. While a reduction of air temperatures does not qualitatively change the sinking and circulation of water masses in our experiments, brine rejection could potentially lead to localized deep water formation. However, the impact is too weak to possibly change the large-scale deep water exchange between the Baltic proper and the northern Baltic sub-basins. Although being in line with established knowledge, through consideration of the model limitations, our results provide insights on how and under which circumstances convective deep water formation could potentially have occurred during cold climate periods. Plain Language Summary The transport of oxygen-rich water into the deep parts of the Baltic Sea is of crucial importance for the ecosystem, as under low-oxygen conditions (hypoxia), most organisms cannot survive and so-called dead zones are formed. The ventilation of Baltic Sea bottom waters is commonly considered to occur solely through inflows of dense, oxygenated water from the North Sea. However, recent analysis of sediment cores and geophysical data suggests the contribution of a second process during cold climate periods: convective deep water formation. This process is initiated through surface cooling or an increase of surface water salinity during sea ice formation (brine rejection) in the winter season. Here, we investigate the role of deep water formation in the northern Baltic Sea in a regional ocean circulation model. We test the influence of reduced air temperatures and consideration of strong, localized brine rejection by performing sensitivity experiments. Generally, our model results do not support the hypothesis of convective deep water formation contributing to the renewal of Baltic Sea bottom waters, but are in line with the established view. Nevertheless, our results provide insights on how and under which circumstances convective deep water formation could potentially have occurred during cold climate periods.

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“…(2020) and also in the high‐resolution multibeam data from R/V Electra presented in Jakobsson et al. (2019).…”

Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Revisiting the Role of Convective Deep Water Formation in Northern Baltic Sea Bottom Water Renewal

et al. 2020

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“…Even so, detecting when the camera revisits a place in 3D space, detecting so called loop closures, remains extremely challenging (Chen, Läbe, et al, 2021;Schönberger & Frahm, 2016). Without an accurate positioning system under water, the described method is limited to 3D Without changing the underlying computational methods, our approach could be extended to other underwater environments, for example the submerged ecosystems of mangrove forests (Giardino et al, 2015), or to guide deep sea exploration & salvage operations (Jakobsson et al, 2021). With the availability of sizeable ego-motion video data from such scenarios, including a reasonably sized dataset of annotated video frames with the classes of interest, our approach should transfer seamlessly to such domains.…”

Section: Discussionmentioning

confidence: 99%

“…Without changing the underlying computational methods, our approach could be extended to other underwater environments, for example the submerged ecosystems of mangrove forests (Giardino et al., 2015), or to guide deep sea exploration & salvage operations (Jakobsson et al., 2021). With the availability of sizeable ego‐motion video data from such scenarios, including a reasonably sized dataset of annotated video frames with the classes of interest, our approach should transfer seamlessly to such domains.…”

Section: Discussionmentioning

confidence: 99%

Scalable semantic 3D mapping of coral reefs with deep learning

Sauder,

Banc‐Prandi,

Meibom

et al. 2024

Methods Ecol Evol

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Coral reefs are among the most diverse ecosystems on our planet, and essential to the livelihood of hundreds of millions of people who depend on them for food security, income from tourism and coastal protection. Unfortunately, most coral reefs are existentially threatened by global climate change and local anthropogenic pressures. To better understand the dynamics underlying deterioration of reefs, monitoring at high spatial and temporal resolution is key. However, conventional monitoring methods for quantifying coral cover and species abundance are limited in scale due to the extensive manual labor required. Although computer vision tools have been employed to aid in this process, in particular structure‐from‐motion (SfM) photogrammetry for 3D mapping and deep neural networks for image segmentation, analysis of the data products creates a bottleneck, effectively limiting their scalability. This paper presents a new paradigm for mapping underwater environments from ego‐motion video, unifying 3D mapping systems that use machine learning to adapt to challenging conditions under water, combined with a modern approach for semantic segmentation of images. The method is exemplified on coral reefs in the northern Gulf of Aqaba, Red Sea, demonstrating high‐precision 3D semantic mapping at unprecedented scale with significantly reduced required labor costs: given a trained model, a 100 m video transect acquired within 5 min of diving with a cheap consumer‐grade camera can be fully automatically transformed into a semantic point cloud within 5 min. We demonstrate the spatial accuracy of our method and the semantic segmentation performance (of at least 80% total accuracy), and publish a large dataset of ego‐motion videos from the northern Gulf of Aqaba, along with a dataset of video frames annotated for dense semantic segmentation of benthic classes. Our approach significantly scales up coral reef monitoring by taking a leap towards fully automatic analysis of video transects. The method advances coral reef transects by reducing the labor, equipment, logistics, and computing cost. This can help to inform conservation policies more efficiently. The underlying computational method of learning‐based Structure‐from‐Motion has broad implications for fast low‐cost mapping of underwater environments other than coral reefs.

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High Emissions of Carbon Dioxide and Methane From the Coastal Baltic Sea at the End of a Summer Heat Wave

et al. 2019

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The summer heat wave in 2018 led to the highest recorded water temperatures since 1926 -up to 21 • C -in bottom coastal waters of the Baltic Sea, with implications for the respiration patterns in these shallow coastal systems. We applied cavity ringdown spectrometer measurements to continuously monitor carbon dioxide (CO 2 ) and methane (CH 4 ) surface-water concentrations, covering the coastal archipelagos of Sweden and Finland and the open and deeper parts of the Northern Baltic Proper. This allowed us to (i) follow an upwelling event near the Swedish coast leading to elevated CO 2 and moderate CH 4 outgassing, and (ii) to estimate CH 4 sources and fluxes along the coast by investigating water column inventories and air-sea fluxes during a storm and an associated downwelling event. At the end of the heat wave, before the storm event, we found elevated CO 2 (1583 µatm) and CH 4 (70 nmol/L) concentrations. During the storm, a massive CO 2 sea-air flux of up to 274 mmol m −2 d −1 was observed. While water-column CO 2 concentrations were depleted during several hours of the storm, CH 4 concentrations remained elevated. Overall, we found a positive relationship between CO 2 and CH 4 wind-driven sea-air fluxes, however, the highest CH 4 fluxes were observed at low winds whereas highest CO 2 fluxes were during peak winds, suggesting different sources and processes controlling their fluxes besides wind. We applied a box-model approach to estimate the CH 4 supply needed to sustain these elevated CH 4 concentrations and the results suggest a large source flux of CH 4 to the water column of 2.5 mmol m −2 d −1 . These results are qualitatively supported by acoustic observations of vigorous and widespread outgassing from the sediments, with flares that could be traced throughout the water column penetrating the pycnocline and reaching the sea surface. The results suggest that the heat wave triggered CO 2 and CH 4 fluxes in the coastal zones that are comparable with maximum emission rates found in other hot spots, such as boreal and arctic lakes and wetlands. Further, the results suggest that heat waves are as important for CO 2 and CH 4 sea-air fluxes as the ice break up in spring.

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Bathymetric Properties of the Baltic Sea

Cited by 3 publications

References 38 publications

Revisiting the Role of Convective Deep Water Formation in Northern Baltic Sea Bottom Water Renewal

Revisiting the Role of Convective Deep Water Formation in Northern Baltic Sea Bottom Water Renewal

Scalable semantic 3D mapping of coral reefs with deep learning

High Emissions of Carbon Dioxide and Methane From the Coastal Baltic Sea at the End of a Summer Heat Wave

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