Air-to-Sea Fluxes of Lipids at Enewetak Atoll

O. C. Zafiriou, R. B. Gagosian, E. T. Peltzer and J. B. Alford
Department of Chemistry
Woods Hole Oceanographic Institution
Woods Hole, MA 02543, USA.

T. Loder
Department of Earth Sciences
University of New Hampshire
Durham, NH 03824, USA.

Journal of Geophysical Research (1985) 90: 2409-2423.

Received: 26 March 1984.
Revised: 11 September 1984.
Accepted: 8 October 1984.
Published: 20 February 1985.


ABSTRACT

We report data for the Enewetak site of the SEAREX program from the rainy season in 1979. The concentrations of n-alkanes, n-alkanols, sterols, n-alkanoic acids and their salts, and total organic compounds in rain are reported, as well as the apparent gaseous hydrocarbon concentrations. These data and information on the particulate forms are analyzed in conjunction with ancillary chemical and meteorological data to draw inferences about sources, fluxes, and chemical speciations. While the higher molecular weight lipid biomarker components are exclusively terrestrial, the organic carbon in rain may be derived from atmospheric transformations of terrestrial carbon. Distinctively marine components are nearly absent. Comparison of the scavenging ratios of the organic components in rain vs. those for clays reveals that the alkanoic acids and the higher molecular weight alkanols behave as essentially particulate materials, whereas the lower alkanols and most hydrocarbons show much higher scavenging ratios, probably due to the involvement of a gaseous phase or sampling artifact. Vaporization in the atmosphere and scavenging of a gas phase would lead to higher scavenging ratios; vaporization during sampling would give low aerosol concentrations and high gas-phase concentrations, leading to high scavenging ratios. The major fluxes at Enewetak result from rain rather than dry deposition, and extrapolating the measured values to meaningful annual averages requires adjustment for seasonally varying source intensity and rain dynamics. Aerosol data for other seasons and other substances are used to correct for source-strength variations, and a Pb-210/organic compound correlation is established and extrapolated to adjust for rainfall volume effects. These corrections, assumed independent and applied together, yield inferred fluxes 2.5-9 times larger that the fluxes calculated for mean concentrations. The inferred fluxes to the ocean, while small compared to primary production, are large enough to have potential impacts in the cycle of dissolved organic carbon and the sedimentary geochemistry of refractory lipid components.


Acknowledgements

This work was supported by National Science Foundation grants OCE 77-12914 and OCE 81-11947. We are grateful to the Mid-Pacific Marine Laboratory for major logistical assistance during the field work phase. We thank N. M. Frew for help with GC-MS work and Elliot Atlas, Patrick Buat-Menard and Paul Doskey for critical comments; we acknowledge many useful comments from and discussions with our SEAREX colleagues. We thank the People's Republic of China for loess and the 700-mbar winds for assistance in transport. This is Woods Hole Oceanographic Institution contribution 5638.


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