Caroline Island - Geography and Climate

Geography and Climate

Caroline Atoll lies near the southeastern end of the Line Islands, a string of atolls extending across the equator some 1,500 km (930 mi) south of the Hawaiian Islands in the central Pacific. The slightly crescent-shaped atoll (3.76 km² or 1.45 mi² in land area) consists of 39 separate islets surrounding a narrow lagoon, 8.7 by 1.2 km² in size, or with an area of 6.3 km². The total atoll area, including dry land, lagoon and reef flat, measures 13 by 2.5 km, or 24 km². The islets rise to a height of only 6 meters (20 ft) above sea level. The islets, like those of all atolls, share a common geologic origin and consist of sand deposits and limestone rock set atop a coral reef.

Three large islets make up the bulk of Caroline's land area: Nake Islet (1.04 km² or 0.40 mi²) at the north; Long Islet (0.76 km² or 0.29 mi²) at the northeast of the lagoon and South Islet (1.07 km² or 0.41 mi²). The remaining assembly of small islets, most of which were named during the 1988 ecological survey, conducted by Angela and Cameron Kepler, fall into four major groupings: the South Nake Islets, the Central Leeward Islets, the Southern Leeward Islets, and the Windward Islets (see map). Caroline's islets are particularly ephemeral— over the course of a century of observation, several of the smallest islets have been documented to appear or disappear entirely following major storms, while the shapes of larger ones have significantly changed.

The central lagoon, roughly 6 km by 0.5 km (3.5 miles by 0.3 miles), is shallow – at most 5–7 m (15–25 ft) in depth – and is crossed repeatedly by narrow coral heads and patch reefs. Reef flats generally extend about 500 m (1600 ft) from shore— although some sources report them to extend more than a kilometer from land— and make boat landings perilous except at high tide. There are no natural landings, anchorages, or deep water openings into the central lagoon; water which spills into the lagoon over shallow channels at high tide is contained within the surrounding reef and remains stable despite ocean tides. Most landings are generally made at a small break in the reef at the northwest corner of the South Islet (visible on the satellite photo above).

There is no standing fresh water on Caroline Island, although the Nake and South Islets harbor underground freshwater aquifers (or Ghyben-Herzberg lenses), and wells have been built to tap drinking water for temporary settlements. Soils on Caroline are similarly poor, dominated by coral gravel and sand, with significant organic content present only within stable, forested island centers. Guano deposits make island soil, where it does exist, nitrogen-rich; but even in the oldest and most vegetated regions of the atoll, soils are only a few centimeters (one or two inches) thick.

Like the rest of Kiribati, Caroline Island enjoys a tropical maritime climate which is consistently hot and humid. Meteorological records are sparse, but temperatures generally range between 28 and 32 degrees Celsius (82 and 90 degrees Fahrenheit) year round. Caroline lies within a region of highly variable precipitation, but is estimated to receive an average of 1500 mm (60 in) of rain annually. Tides are on the order of 0.5 m (1.5 ft) and trade winds, generally from the northeast, mean that corner of the island experiences the roughest seas.

Caroline Island is among the most remote islands on earth–230 km (140 mi) from the closest land at Flint Island, 1,500 km (930 mi) from the nearest permanent settlement on Kiritimati, 4,200 km (2,600 mi) from the Kiribati capital of Tarawa, and 5,100 km (3,200 mi) from the nearest continental land in North America.