Cold water upwelling and entrainment near the Anadyr Strait: Implications to the North Pacific-Arctic interaction

The Tenth Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Wed. 4 Dec. / Entrance Hall (1st floor) , National Institute of Polar Researc

Recent sediment dynamics in hadal trenches: evidence for the influence of higher-frequency (tidal, near-inertial) fluid dynamics

http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk10-16/ehttp://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk12-09/

Vertical fluxes of nutrients enhanced by strong turbulence and phytoplankton bloom around the ocean ridge in the Luzon Strait

Abstract Steep oceanic ridges and tidal currents in the Luzon Strait generate some of the world’s strongest turbulent mixing. To evaluate the impacts of the turbulence intensity on the marine ecosystem, we carried out measurements of microstructure turbulence and biogeochemical hydrography along 21°N in the Luzon Strait during the R/V Hakuho Maru cruise, KH-17-5-2, in November 2017. We found a turbulent kinetic energy dissipation rate exceeding O(10−7) W kg−1 and vertical eddy diffusivity exceeding O(10−3) m2 s−1, two orders of magnitude larger than those in the open ocean, above a shallow sub-ridge on the eastern ridge of the Luzon Strait. In addition, a clear chlorophyll a bloom was identified in the surface layer above the sub-ridge from in situ measurements and satellite observations. High values of nitrate (4.7 mmol N m−2 d−1) and phosphate (0.33 mmol P m−2 d−1) fluxes estimated near the base of the surface chlorophyll a bloom strongly suggest that enhanced turbulent mixing promotes nutrient supply to the euphotic zone and generates new production within the surface layer, contributing to the formation of a quasi-permanent local chlorophyll a bloom north of Itbayat Island on the eastern ridge

Recent sediment dynamics in hadal trenches:evidence for the influence of higher-frequency (tidal, near-inertial) fluid dynamics

In addition to high hydrostatic pressure, scarcity of food is viewed as a factor that limits the abundance and activity of heterotrophic organisms at great ocean depths, including hadal trenches. Supply of nutritious food largely relies on the flux of organic-rich particulate matter from the surface ocean. It has been speculated that the shape of hadal trenches helps to 'funnel' particulate matter into the deeper parts of the trench, leading to sediment 'focussing' and improved benthic food supply. Here we investigate for five Northwest Pacific trenches the efficiency of sediment focussing by evaluating ratios of measured (sediment-derived) and expected (water-column-derived) sedimentary inventories of the naturally occurring and radioactive particulate-matter tracer Pb-210(xs). The sites comprise a broad range of surface-ocean productivity and physical-oceanographic regimes. Across the five trench-axis settings the inventory ratio varies between 0.5 and 4.1, with four trench-axis settings having ratios > 1 (sediment focussing) and one trench-axis setting a ratio < 1 (sediment winnowing). Although the fluid- and sediment-dynamical forcing behind sediment focussing remains unclear, this study finds evidence for another mechanism that is superimposed on, and counteracts, the focussing mechanism. This superimposed mechanism is related to higher-frequency (tidal, near-inertial) fluid dynamics. In particular, there is evidence for a strong and negative relation between the intensity of propagating internal tides and the extent of sediment focussing in the trench-axis. The relation can be approximated by a power function and the most intense drop in sediment focussing already occurs at moderate internal-tide intensities. This suggests that propagating internal tides may have a subtle but significant influence on particulate-matter dynamics and food supply in hadal trenches in particular, but possibly also in the deep seas in general. A mechanism for the influence of internal tides on sediment dynamics is proposed. (C) 2014 Elsevier Ltd. All rights reserved