Micro-organisms as indicators of hydrological phenomena in seas and oceans—III

• 1.

  (1) A study of the vertical distribution of the numbers of heterotrophs was carried out at 56 stations in the Pacific Ocean along two parallel sections (174°W and 172°E from 37°N to 41 °S). The equatorial-tropical zone is distinguished by a relative abundance of heterotrophs assimilating only easily accessible organic matter.

• 2.

  (2) The equatorial-tropical waters are found at various subsurface levels in the sub-tropical areas. A very thick layer was observed in the northern hemisphere along 172°E where it was carried northwards by the Kuroshio current. Some strata of equatorial-tropical waters were also detected at considerable depths (6000–7000 m, 7500–9000 m) in the Kermadec trench.

• 3.

  (3) In the equatorial zone two layers of water, 375–550 m and 700–1800 m, were similar in their organic content to Arctic and Antarctic waters, these layers expanded considerably north and south from the equatorial zone. This circulation of waters from high latitudes across the equator also occurs in much deeper layers, judging from a layer of water with few heterotrophs observed near the equator at depths of 2500–4500 m.