The dependence of upper ocean gyres on wind and buoyancy forcing

A series of numerical simulations with different forcing conditions are carried out, to investigate the roles played by buoyancy and wind forcing on the upper ocean gyres, and to contrast the laminar and eddying regimes. Model experiments show that the buoyancy-driven eastward geostrophic flow tends to suppress the formation of the wind-driven subpolar gyre, but the northward eddy heat transport can homogenize the subpolar water and reduce the meridional temperature gradient by about two-third, thus counteracting the buoyancy effect and saving the subpolar gyre. For the subtropical gyre, its transport is enhanced by eddy mixing, and the role of buoyancy forcing is very sensitive to the choice of diapycnal diffusivity. Our results suggest that eddy effects must be considered in the dynamics of the subpolar gyre, and vertical diffusivity should be selected carefully in simulating the basin-wide circulations.

Gateway-driven weakening of ocean gyres leads to Southern Ocean cooling

Declining atmospheric CO2 concentrations are considered the primary driver for the Cenozoic Greenhouse-Icehouse transition, ~34 million years ago. A role for tectonically opening Southern Ocean gateways, initiating the onset of a thermally isolating Antarctic Circumpolar Current, has been disputed as ocean models have not reproduced expected heat transport to the Antarctic coast. Here we use high-resolution ocean simulations with detailed paleobathymetry to demonstrate that tectonics did play a fundamental role in reorganising Southern Ocean circulation patterns and heat transport, consistent with available proxy data. When at least one gateway (Tasmanian or Drake) is shallow (300 m), gyres transport warm waters towards Antarctica. When the second gateway subsides below 300 m, these gyres weaken and cause a dramatic cooling (average of 2–4 °C, up to 5 °C) of Antarctic surface waters whilst the ACC remains weak. Our results demonstrate that tectonic changes are crucial for Southern Ocean climate change and should be carefully considered in constraining long-term climate sensitivity to CO2.

Global biogeography of living brachiopods: Bioregionalization patterns and possible controls

The global distribution patterns of 14918 geo-referenced occurrences from 394 living brachiopod species were mapped in 5° grid cells, which enabled the visualization and delineation of distinct bioregions and biodiversity hotspots. Further investigation using cluster and network analyses allowed us to propose the first systematically and quantitatively recognized global bioregionalization framework for living brachiopods, consisting of five bioregions and thirteen bioprovinces. No single environmental or ecological variable is accountable for the newly proposed global bioregionalization patterns of living brachiopods. Instead, the combined effects of large-scale ocean gyres, climatic zonation as well as some geohistorical factors (e.g., formation of land bridges and geological recent closure of ancient seaways) are considered as the main drivers at the global scale. At the regional scale, however, the faunal composition, diversity and biogeographical differentiation appear to be mainly controlled by seawater temperature variation, regional ocean currents and coastal upwelling systems.

Conversion of Marine Litter from Venice Lagoon into Marine Fuels via Thermochemical Route: The Overview of Products, Their Yield, Quality and Environmental Impact

Plastics floating in ocean gyres are a popular topic within pollution discussion; however, no simple solution exists to deal with marine litter. Overcoming limitations in collection, and perhaps even more in the environmentally, technically and economically acceptable use of the collected material, is of paramount importance. This paper presents initial results from converting plastic marine litter processed as-is, without pretreatment, and sorting into marine gas oil (MGO) compliant with the ISO8217 DMA standard via a pyrolysis and distillation process. Yields, composition and key properties of products along with levels of eight environmental contaminants potentially generated by the process are presented. More than 100 kg of actual marine litter from the Venice Lagoon, including polyolefins packaging and polyamides fishing nets, were converted into products at approximately 45 wt% yield of which approximately 50% (V/V) was MGO. By our knowledge, this is the first report of chemical recycling of real marine litter targeting the production of standardized marine fuels beyond laboratory scale, outlining coarse but realistic figures finally available as an initial benchmark. The process supports the concept of circularity in the blue economy and could be employed to tackle difficult terrestrial plastic waste to help prevent marine litter generation.

Meridional changes in the South Atlantic Subtropical Gyre during Heinrich Stadials

Subtropical ocean gyres play a key role in modulating the global climate system redistributing energy between low and high latitudes. A poleward displacement of the subtropical gyres has been observed over the last decades, but the lack of long-term monitoring data hinders an in-depth understanding of their dynamics. Paleoceanographic records offer the opportunity to identify meridional changes in the subtropical gyres and investigate their consequences to the climate system. Here we use the abundance of planktonic foraminiferal species Globorotalia truncatulinodes from a sediment core collected at the northernmost boundary of the South Atlantic Subtropical Gyre (SASG) together with a previously published record of the same species from the southernmost boundary of the SASG to reconstruct meridional fluctuations of the SASG over last ca. 70 kyr. Our findings indicate southward displacements of the SASG during Heinrich Stadials (HS) 6-4 and HS1, and a contraction of the SASG during HS3 and HS2. During HS6-4 and HS1, the SASG southward displacements likely boosted the transfer of heat to the Southern Ocean, ultimately strengthening deep-water upwelling and CO2 release to the atmosphere. We hypothesize that the ongoing SASG poleward displacement may further increase oceanic CO2 release.

Microplastics as contaminants in marine environment

ABSTRACT Since the mass production of plastics began in the 1940s, microplastic contamination of the marine environment has been a growing problem. Here, a review of the literature has been conducted with the following objectives: To summarise what are microplastics; To discuss the routes by which microplastics enter the marine environment; To assess spatial and temporal trends of microplastic abundance; to discuss the environmental impact of microplastics; and remedial measures; Microplastics are both abundant and widespread within the marine environment, found in their highest concentrations along coastlines and within mid-ocean gyres. Ingestion of microplastics has been demonstrated in a range of marine organisms, a process which may facilitate the transfer of chemical additives or hydrophobic waterborne pollutants to biota. A case study has also been done about the ingestion of microplastics by zooplankton groups in Kenya’s marine environment. We conclude by highlighting key future research areas for scientists and policymakers. Keywords—Micro plastics; marine organisms; marine environment

The Trash Tracker: A Macroplastic Fate and Transport Model at River Basin Scale

<p>Plastic pollution in terrestrial and aquatic ecosystems is of growing global concern due to its negative impact on environmental health and human livelihood. Most plastic research to date focused on observing and modelling plastic in the oceans, revealing that the highest plastic concentrations are found in the five ocean gyres (“the garbage patches”). Plastic waste originating from land has been identified as the main source of marine plastic debris. Yet it remains highly uncertain which processes control the mobilisation and transport of plastic waste over land to rivers and eventually to the ocean. Here, we introduce the Trash Tracker, a numerical model to forecast the pathways and fate of plastic waste in terrestrial and freshwater systems. In this model, the plastic transporting agents, wind and surface runoff, are resisted by the friction of the terrain. The terrain resistance, a function of the surface slope and the type of land use, is translated to thresholds that define the critical wind and surface runoff conditions required to mobilise and transport macroplastics. By repeatedly checking whether the wind and/or surface runoff conditions are strong enough to overcome their respective thresholds, the Trash Tracker simulates the transport of plastics and allows us to identify accumulation hotspots and high probability transport routes of plastic waste within river basins. This makes the Trash Tracker a practical tool for preventing, mitigating and reducing plastic pollution in the natural environment.</p>