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Understanding the Environment
Published in Julie Kerr, Introduction to Energy and Climate, 2017
The North Pacific Subtropical Gyre helps confine the Great Pacific Garbage Patch. By definition, an ocean gyre is a system of circular ocean currents formed by the earth’s wind patterns and the forces created by the earth’s rotation. In this case, the North Pacific Subtropical Gyre is created by the proximal interaction of the California, North Equatorial, Kuroshiro, and North Pacific currents. All four currents move in a clockwise direction around an area of approximately 7.7 million square miles (20 million km2) in size. In a gyre, the currents on the outside are actively moving, but the area inside the borders of the currents is very stable. This is where the garbage is currently being trapped and deposited. For example, if someone throws a plastic water bottle into the ocean from the coast of California, it will join the California Current and travel southward toward Mexico. From there, it could enter the North Equatorial Current and head across the Pacific Ocean. If the bottle reaches Japan and then gets swept up in the Kuroshiro Current, it can be carried to the north, to eventually be intercepted by the westward North Pacific Current. The two vortexes—the Eastern and Western Garbage Patches—will eventually capture the bottle (Figure 1.3).
Managing conflicts of interest
Published in Peter B. Myles, Maritime Clusters and the Ocean Economy, 2017
The Sargasso Sea Alliance report (2009), entitled ‘The protection and management of the Sargasso Sea’, provides a summary of the scientific and other supporting evidence for the importance of the Sargasso Sea and is intended to: develop international recognition; start the process of establishing appropriate management and precautionary regimes within existing agreements; and stimulate a wider debate on appropriate management and protection for the high seas. The Sargasso Sea is a place of legend with a rich history of great importance to Bermuda. Other attributes of the Sargasso Sea, as described in the report, include: It is an iconic ecosystem based upon floating Sargassum, the world’s only holopelagic seaweed, hosting a rich and diverse community including ten endemic species.It provides an essential habitat for nurturing a wide diversity of species, many of which are endangered or threatened.It is the only breeding location for the threatened European and American eels.It lies within a large ocean gyre which concentrates pollutants and which has a variety of oceanographic processes that impact its productivity and species diversity.It plays a disproportionately large role in global ocean processes of carbon sequestration.It is of major importance for global scientific research and monitoring and is home to the world’s longest ocean time series of measurements.It has significant values to local and worldwide economies.It is threatened by activities including overfishing, pollution, shipping and Sargassum harvesting.
Scientific ocean drilling in the Australasian region: a review
Published in Australian Journal of Earth Sciences, 2022
IODP Expedition 329 in the western Pacific east of New Zealand was a major study of the limits of microbial life at depth, with deliberate selection of the lowest productivity area in the world oceans. Seven widespread sites in abyssal depths beneath the South Pacific Gyre explored the nature of subseafloor sedimentary communities and habitats in the low-activity heart of an open ocean gyre, the least habitable region. Microbial cell counts were lower by three or more orders of magnitude at the same sediment depths than in all sites previously cored by scientific ocean drilling. Countable cells disappeared with increasing depth in the sediment. Concentrations of dissolved oxygen and nitrate, total organic carbon, and total nitrogen stabilised as countable cells fell below the minimum detection limit at <15 mbsf.
The modeling of the equatorial undercurrent using the Navier–Stokes equations in rotating spherical coordinates
Published in Applicable Analysis, 2021
The shallow-water limit corresponds to the limiting process and (see the discussion in [19]). This regime ignores the vertical velocity component and, neglecting wave perturbations by setting h = 0, the flow dynamics being governed by the horizontal flow components u and v, subject to the nonlinear system which features Coriolis terms, viscous terms and the horizontal pressure gradients, while the boundary conditions (11)–(13) simplify to since setting w = 0 and h = 0 makes (12) irrelevant. The system (16)–(20) captures the physical idea that the perturbation of the hydrostatic pressure and the shear stresses and , at the ocean's surface z = 0, are needed to produce a consistent solution for the wind-drift horizontal current . To gain insight into the structure of this system, let us note that (18) ensures (see the discussion in [23]) the existence of a stream function in spherical coordinates, , with see [23] for a proof of the fact that the particle paths for steady flow on the surface of a sphere are the level sets ψ=constant. Taking advantage of (21), we can eliminate the pressure between Equations (16) and (17) to derive (see [19]) the vorticity equation These considerations show that (21) specifies, at leading order, the background flow, provided that the stream function solves the vorticity equation (22) subject to the boundary condition (19) and to the last two constraints in (20); Equations (16)–(17) then determine the associated pressure field, taking also into account the boundary condition represented by the first constraint in (19). Let us note that if we ignore the z-dependence (and thus, implicitly, consider an inviscid setting in which the wind forcing plays no role), then (22) simplifies to the ocean gyre model derived recently in [24] as a shallow-water asymptotic solution of Euler's equation in rotating spherical coordinates (with the stipulation that θ stands in [24] for the polar angle, and not for the angle of latitude) and further investigated in [25–29] in the context of the Antarctic Circumpolar Current – the largest ocean current on Earth, flowing clockwise from west to east around Antarctica (see [30,32,37]) so that, due to the lack of any landmass connecting with Antarctica, it keeps the warm ocean waters from lower latitudes away from Antarctica and thus maintains the huge ice sheets encountered near the South Pole (see the discussion in [13,31]).