18 research outputs found
Propagation and transformation of upper North Atlantic deep water from the subpolar gyre to 26.5°N
Because new observations have revealed that the Labrador Sea is not the primary source for waters in the lower limb of the Atlantic Meridional Overturning Circulation (AMOC) during the Overturning in the Subpolar North Atlantic Programme (OSNAP) period, it seems timely to re‐examine the traditional interpretation of pathways and property variability for the AMOC lower limb from the subpolar gyre to 26.5°N. In order to better understand these connections, Lagrangian experiments were conducted within an eddy‐rich ocean model to track upper North Atlantic Deep Water (uNADW), defined by density, between the OSNAP line and 26.5°N as well as within the Labrador Sea. The experiments reveal that 77% of uNADW at 26.5°N is directly advected from the OSNAP West section along the boundary current and interior pathways west of the Mid‐Atlantic Ridge. More precisely, the Labrador Sea is a main gateway for uNADW sourced from the Irminger Sea, while particles connecting OSNAP East to 26.5°N are exclusively advected from the Iceland Basin and Rockall Trough along the eastern flank of the Mid‐Atlantic Ridge. Although the pathways between OSNAP West and 26.5°N are only associated with a net formation of 1.1 Sv into the uNADW layer, they show large density changes within the layer. Similarly, as the particles transit through the Labrador Sea, they undergo substantial freshening and cooling that contributes to further densification within the uNADW layer
Regional Imprints of Changes in the Atlantic Meridional Overturning Circulation in the Eddy-rich Ocean Model VIKING20X
A hierarchy of global 1/4° (ORCA025) and Atlantic Ocean 1/20° nested (VIKING20X) ocean/sea-ice models is described. It is shown that the eddy-rich configurations performed in hindcasts of the past 50–60 years under CORE and JRA55-do atmospheric forcings realistically simulate the large-scale horizontal circulation, the distribution of the mesoscale, overflow and convective processes, and the representation of regional current systems in the North and South Atlantic. The representation, and in particular the long-term temporal evolution, of the Atlantic Meridional Overturning Circulation (AMOC) strongly depends on numerical choices for the application of freshwater fluxes. The interannual variability of the AMOC instead is highly correlated among the model experiments and also with observations, including the 2010 minimum observed by RAPID at 26.5° N pointing at a dominant role of the forcing. Regional observations in western boundary current systems at 53° N, 26.5° N and 11° S are explored in respect to their ability to represent the AMOC and to monitor the temporal evolution of the AMOC. Apart from the basin-scale measurements at 26.5° N, it is shown that in particular the outflow of North Atlantic Deepwater at 53° N is a good indicator of the subpolar AMOC trend during the recent decades, if the latter is provided in density coordinates. The good reproduction of observed AMOC and WBC trends in the most reasonable simulations indicate that the eddy-rich VIKING20X is capable in representing realistic forcing-related and ocean-intrinsic trends
Restricted dispersal in a sea of gene flow
Howfar domarine larvae disperse in the ocean? Decades of population genetic
studies have revealed generally low levels of genetic structure at large spatial
scales (hundreds of kilometres). Yet this result, typically based on discrete
sampling designs, does not necessarily imply extensive dispersal. Here, we
adopt a continuous sampling strategy along 950 km of coast in the northwestern
Mediterranean Sea to address this question in four species. In line
with expectations, we observe weak genetic structure at a large spatial scale.
Nevertheless, our continuous sampling strategy uncovers a pattern of isolation
by distance at small spatial scales (few tens of kilometres) in two species. Individual-
based simulations indicate that this signal is an expected signature of
restricted dispersal. At the other extreme of the connectivity spectrum, two
pairs of individuals that are closely related genetically were found more
than 290 km apart, indicating long-distance dispersal. Such a combination of
restricted dispersal with rare long-distance dispersal events is supported by
a high-resolution biophysical model of larval dispersal in the study area,
and we posit that it may be common in marine species. Our results bridge
population genetic studies with direct dispersal studies and have implications
for the design of marine reserve networksVersión del edito
Mixing and Circulation in the Tropical Atlantic Cruise No. M98
July 01 – July 28, 2013
Fortaleza (Brazil) – Walvis Bay (Namibia
Lagrangian ocean analysis: fundamentals and practices
Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing
Biodegradation of diesel oil in marine environment by a floating water droplet
© 2017, Islamic Azad University (IAU). Diesel oil is one of the derivatives of crude oil which resistance to biodegradation due to its complex structure and low solubility in water. A novel concept of enhancement of diesel degradation using floating water droplet is proposed and being investigated to address some key challenges encountered in diesel oil spillages in the aqueous area and wetlands. This study aims to increase the floatability of a floating water droplet on oil. A droplet containing a mixed consortium of 60 different hydrocarbon degrading bacteria and sodium dodecyl sulfate as a surfactant was deposited on the diesel oil surface. Contact angle and contact radius were monitored to observe the effect of bacterial activities on the droplet. The behavior of this droplet on diesel oil was different to a previous study with paraffin oil. In particular, the floatability, bacterial growth and biofilm formation demonstrate significant deviation due to the diesel interactions with biological processes. Nevertheless, the results show this method increase microbial activities within the droplet. The result verifies the applicability of the floating water droplet as an environmentally friendly method for diesel oil spillages