Georgia Tech Southern Line Islands Expedition
Caroline, Malden & Flint Islands
October 30 - November 20, 2008

For slideshow of the cruise, click here

About the Expedition

We conducted a three-week long scientific cruise expedition to visit three remote islands in the southern Line Islands chain of the Republic of Kiribati (Caroline, Malden and Flint Islands; 4-11S, 150-154W) aboard the R/V Bounty Bay in November 2008. The objectives of the expedition were to survey corals in these rarely visited islands and investigate the signature of anthropogenic forcing on tropical Pacific temperature and rainfall using coral -derived climate records. Coral surveys and cores retrieved from the expedition complement our previous work in the northern Line Islands (Palmyra, Fanning and Christmas Islands) [Cobb et al., 2003; Nurhati et al, 2009]. Our Georgia Tech team of three scientists (Intan Suci Nurhati, Jordan Watson and Branwen Williams) conducted coral survey on the leeward sides of each island via towing method, and retrieved the coral cores from ~10 m depth using underwater hydraulic drilling equipment via SCUBA. We installed automatic temperature loggers at each island that are recording in situ temperature for the next three years We hope to retrieve these devices on future trips organized by us or our collaborators. During the expedition, we also conducted land survey and collected fossilized coral deposits in hopes of extending the length of the climate record beyond the last century. Several gorgonian soft corals were also collected from ~40 m depth as an alternative archive for past climate changes. Along the cruise track, we conducted oceanographic measurements (sea-surface temperature and salinity) and collected seawater sampling at every one degree latitudes as well as at each island that will serve as calibrations for our coral-derived climate records.

The absence of massive brain Porites corals that would provide a very long climate archive from these islands was surprising as well as alarming, given their relative abundance in the Northern Line Island chain. While it may be partly due to the oceanographic conditions (cooler sea-surface temperatures, stronger currents and wave activity), it might also be related to anthropogenic global warming and/or ocean acidification that have stressed these already marginal coral reef environments to the point of decreased diversity and coral colony size.

References
Cobb, K. M., Charles, C. D., Cheng, H.,& Edwards, R. L. (2003). El Nino/Southern Oscillation and tropical Pacific climate during the last millennium. Nature 424, 271-276.
Nurhati, I.S., Cobb, K. M., Charles, C. D., & Dunbar, R. D. (2009). Late 20th century warming and freshening in the central tropical Pacific. Geophysical Research Letters, 36, L21606, doi:10.1029/2009GL040270.

Caroline Island (10S, 150W)

Caroline Island was the first island we visited during the cruise, where we spent 2 days conducting underwater coral survey and drilling. We approached the island from south, and cruised along its leeward/west side while observing and taking photographs of the island before anchored our boat on the northwest side of the island. The island has thick vegetations due to high mean rainfall of 1500 mm/year. The island is comprised of several islets, and has numerous fossil coral deposits scattered in its tidal flats and lagoons. Red-algae covered reef formations surround the islets, making landing really difficult. Caroline Island has healthy coral reef with high coral cover (>90%) and high biodiversity of corals and fishes, as well as high abundance of shark populations most notably the black-tip reef sharks.

From Caroline, we continued north towards Malden where we spent 3 days conducting underwater and land works. We approached the island from south, cruised along its leeward/west side and anchored on its northwest side where there is a wide extent of wide beach area, making landing relatively easy. The island is a tropical desert with a mean rainfall of 667 mm/year with vegetation mostly in the form of bushes, and a few coconut trees near the abandoned settlement compound.
Malden has poor coral condition (50-70% coral cover), and low biodiversity of corals and coral fishes. The island is bathed by the colder equatorial upwelling seawater (27 deg C), and is characterized by more energetic wave activity even on the leeward side where our boat was anchored. We observed that coral coverage can vary appreciably from one area to another. While one area may have very low coral coverage and poor coral conditions, another area may be almost completely covered by Acropora sp., while yet another area has several massive colonies of plate morphology Porites corals.
During land work, we observed massive fossilized corals scattered over a vast bushy area which may have been a dried lagoon, as well as dunes of coral rubbles that were washed onshore during strong storms. Branching and plate morphologies seem to be the dominant forms of both modern/living and fossil corals in Malden Island.

On our southbound leg returning to Papeete, we approached Flint Island from the north and anchored on its northwest side. Similar to Caroline in latitude, Flint is also thickly vegetated with trees. It is a very narrow island with a narrow lagoon surrounding the island. Landing is also difficult; however, visitors may utilize the existing dynamited passage located in its northwest side.
Flint has good coral condition with approximately >85% coral cover and fairly good biodiversity. The island has a large sea-turtle population (we counted 16 of them on our 1.5 hours survey transect). Despite good coral diversity, the coral colonies are uniformly small and the shark populations are not as abundant as those from Caroline Island. Flint was once a base of significant human activities associated with guano harvesting and coconut plantations, as well as fairly recent fishing activity.