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Swimmers: A Recapitulation of the Problem and a Potential Solution

D. Karl,G. A. Knauer

Published 1989 in Oceanography

ABSTRACT

W E READ, with great interest, the article by Lee et uL (I 988) concerning the effects of "'swimmers'" on the measurement of particulate organic matter flux in the marine environment. Generally swinnners are either: (1) acknowledged and their impact reduced by manually removing the carcasses ("picking") before further sample processing, (2) acknowledged, but trap contents analyzed unaltered, or (3) totally ignored. None of these three options is acceptable, if the desired outcome is to obtain accurate particle flux estimates. As Lee etal. (1988) discuss in their review, the swimmer problem is exacerbated in near-surface waters (<500 m). Unfortunately, the measurement of particulate organic matter flux in the upper water column is crucial to our understanding of biogenic element cycles, including the rates and mechanisms of nutrient regeneration and, consequently, crucial to addressing the Global Ocean Flux Study (GOFS) program objectives (Brewer et al., 1986). Because sediment traps are now recognized as the only method for estimating the passive downward flux of organic matter in the sea (SCOR WG-71 report on "Particulate Biogeochemical Processes," S. Krishnaswami, chairman), our progress toward a resolution of these important oceanic processes is stalled at this time. So, to provide a brief answer to the rhetorical question posed in their title, "Are %wirereefs" a Problem?," we believe the reply is an overwhelming affirmative. In fact, the problem of swimmers may be more severe than stated in the Lee etal. (1988) review. To date, most measurements of sediment trap-collected materials have focused on the particulate phase. However, it is well known that a finite but variable percent of the biogenic materials collected by sediment traps may partition into the solute phase (Knauer e t u l , 1979; Knaueretal . . 1984). The extent to which the particulate constituents disaggregate/disintegrate, dissolve, hydrolyse or remineralize after entering the sediment trap will depend upon a number of complex variables that are not understood at the present time. If one ignores the solute phase during sample processing, one will certainly underestimate the true

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