22
3.5
Environmental Aspects of Bikini Atol]
3.5-1
Geography and Hydrology
S*kini Atol] is Tocated in the Central Pacific Ocean
rear TISN latitude, 165°E longitude.
The coralline atoll rises 4600 meters
off the sea floor in the Northern Marshall Islands.
The 629-square kilometer
lagoon area averages 47.5 meters in depth and is enclosed on all sides by an
exposed reef.
An 18.3 meter lagoon terrace divides the deeper lagoon from
tne reef perimeter.
The hydrology of Bikini Lagoon has been the subject of papers by Von Arx
(1948, 1954), Munk and Sargent (1954), Munk, Ewing and Revelle (1949),
Johnson (1949) and Ford (1949).
The model of the winter lagoon circulation
shcvn in Figure 3 resembles a typical wind-driven, two-layer system of inland
labes.
The circulation is driven by the action of wind, waves, tides and the
Ncrth Equatorial Current (Von Arx, 1954).
Year-round entrance of seawater to
the lagoon occurs through passes on the southern perimeter of the reef and is
surplenented during the winter by the tradewinds which force water over the
inter-island reefs during high tide.
The surface waters that do not exhaust
Cyer southern and western passes or reefs sink and form a slower moving return
fic, wnich bifurcates at the eastern portion of the lagoon, forming two deep
meter spirals.
Von Arx (1954) placed the limits of the upwelling zone in the
fertern lagoon at about 2500 meters from the midpoint of the east
reef and as
art £4°7-3399 meters wide.
eee
.
He also found that the direction and speed of
te surface and deep-water components is nearly constant at 3% of the
-
Ye-hour average wind speed.
e7Br loos
This results in an average 9-13 meter
wer Surface layer, with average speeds of 15 and 25 cm/s in the summer
LOtl tae!
;
:
.
wvssran, and winter (tradewind) seasons, respectively (Von Arx, 1954).
seh
wee
The
me current speed is generally thought to be approximately one-third