Dynamics and water mass structure of a summertime anticyclonic eddy in Funka Bay, Hokkaido, Japan

Daisuke Takahashi, Yoshinori Nishida, Kazuyuki Uehara, Hideo Miyake

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)

Abstract

The hydrography and flow structure of an anticyclonic eddy are investigated synoptically using conductivity, temperature and depth (CTD) and Acoustic Doppler Current Profiler (ADCP) data for Funka Bay on June 17 and July 23, 1997. In June, the anticyclonic eddy was characterized by a deep concave structure of isopycnal surfaces, with elliptical horizontal shape. The tangential speed of the eddy at 10m depth approached a maximum of 30cms-1 at a radius of about 10km. In July, the eddy was characterized by a sharp pycnocline with two density fronts around the outer edge of the eddy at a depth of 10m. The horizontal shape of the eddy became circular, and the maximum tangential speed at 10m depth decreased to 25cms-1 at a radius of about 15km. The core of the eddy rotated as a rigid body through one cycle approximately once every 2.3 days in June, and every 4.8 days in July. Analysis of the tangential currents at 10m depth using the gradient flow relationship revealed that the eddy was hydrodynamically balanced between three forces: Coriolis force, centrifugal force and a force due to the horizontal pressure gradient. The vertical and horizontal scales of the eddy changed dramatically between June and July, with the vertical scale of the eddy becoming shallower as the deep concave structure of the isopycnal surfaces was destroyed due to the intrusion of water originating from Tsugaru warm water (TW). The horizontal scale of the eddy also decreased from June to July, related to the formation of two density fronts arising due to coastal upwelling associated with south-southeasterly winds and due to contact of the eddy with water originating from TW in the upper layer. The coastal upwelling not only changed the horizontal structure of the eddy, but also transported nutrients to the surface layers from deeper layers. These nutrients would promote primary production in summer in Funka Bay. The collection of scallop larvae by aquacultural netting at fixed coastal sites would therefore be strongly affected by the eddy, suggesting that the eddy plays an important role in the ecosystem of Funka Bay.

Original languageEnglish
Pages (from-to)185-195
Number of pages11
JournalEstuarine, Coastal and Shelf Science
Volume61
Issue number1
DOIs
Publication statusPublished - 2004 Sep

Keywords

  • Funka Bay
  • anticyclonic eddy
  • coastal upwelling
  • gradient flow
  • intrusion water
  • rigid body rotation

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science

Fingerprint Dive into the research topics of 'Dynamics and water mass structure of a summertime anticyclonic eddy in Funka Bay, Hokkaido, Japan'. Together they form a unique fingerprint.

Cite this