Chapter I Intro & Objectives - SPREP

PHOENIX ISLANDS PROTECTED AREA MANAGEMENT PLAN
Chapter III. Background, 1. Physical Setting of the Islands
Draft 1 March 2007
Henderson et al (1978) reported that the predominant aspects of lagoon circulation on
Abariringa (Canton) were wind drift and tidal flow. Lagoon tide showed a pronounced lag
compared to ocean tides. However, there was no measurable amplitude attenuation from the
ocean to the back lagoon.
Guinther (1978) reported that salinity was moderate (13 to 18 ppt) in channel bid ponds.
Lower salinities (less than 8 ppt) were measured in potholes and water filled burrows in the
surrounding flats. High salinities (greater than 24 ppt and up to 152 ppt) were measured in
two larger ponds in the lagoon tidal channels and in the saltern [saltworks building]. There
was wide variation in nutrient levels and chlorophyll a between sites surveyed.
Smith and Jokiel (1975a and b and 1978) developed a salt and water budget for Abariringa’s
(Canton) lagoon. They estimated that the oldest lagoon water was about 95 days old, the
average residence time was 50 days. They concluded that eddy diffusion was the major
process by which water entered the lagoon on the incoming tide. Lagoon water evaporation
rate at Abariringa (Canton) was about twice that of the open ocean in the vicinity of
Abariringa (Canton).
In the last 8,000 years about 20 m of sediment has been deposited in the lagoon on Abariringa
(Canton) (Smith and Jokiel 1978). Smith and Jokiel (1978) speculated that the entire reef
was not more than 8,000 years old and that it grew from a based maximum depth of about 25
m.
Garnett (1983) reported that the slightly supersaline lagoon was seldom more than 2 m deep
with extensive mudflats and coral patches.
Lagoon Openings - The western side of the island had several openings (Hydrographic Office
1916; two openings according to Hydrographic Office 1940; four openings according to
Bryan 1941 and 1942). One opening was dry during low tide, and two were blocked by coral
heads (Bryan 1941 and 1942; see also Bryan 1974).
A deepwater entrance was dredged through the western rim to allow shall ships to anchor
within the lagoon (Bryan 1974). This was done in 1943 (Degener and Gillaspy 1955). In the
1950s the secondary channel north of the western side was blocked by construction (Obura in
press). Neemia and Thaman (1993) reported that Abariringa (Kanton “in the Line Islands”)
had navigable channel access to the lagoon.
McIntire (1960) noted that there were three channels to the lagoon on Abariringa (Canton),
but causeways were built across the two northernmost channels. The southern channel was
dredged so that vessels could enter the lagoon.
A comparison was made of the changes in lagoon entrances of Abariringa (Canton) by
Henderson et al (1978). Entrances from 1938 and 1973 are compared in Figure III-1.2 below.
Figure III-1.2. Comparison of changes in the lagoon entrances of
Abariringa (Canton) between 1938 and 1973.
(source: Henderson et al 1978).
4