* Corresponding author. E-mail address: gundersen@botan.su.se (K. Gundersen).  Present address. Department of Botany, Stockholm University, Stockholm, Sweden.  Presentaddress.WrigleyInstituteforEnvironmentalStudies,UniversityofSouthernCalifornia,LosAngeles,USA. Deep-Sea Research II 48 (2001) 1697}1718 Particulate organic carbon mass distribution at the Bermuda Atlantic Time-series Study (BATS) site Kjell Gundersen*,KarenM.Orcutt, Duncan A. Purdie, Anthony F. Michaels,AnthonyH.Knap Bermuda Biological Station for Research, St. George's, Bermuda, UK School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, Southampton, UK Abstract Errorsintotalparticulateorganiccarbon(totalPOC)measurementscausedbyparticlessettlinginNiskin water samplers, loss of bacterial cells during "ltration and undersampling of rare particles such as the diazotrophic cyanobacterium Trichodesmium spp. were investigated at the Bermuda Atlantic Time-series Study(BATS)site.Regularcoresamplesoftemperature,primaryproduction,bacterialabundance,chloro- phyll-a (Chl-a)andPOCwerecollectedatmonthlyintervalsfrom1991to1996.Duringthisperiodoftime, shorterinvestigationsofparticlessettlinginwatersamples(1991}1992),bacterialcellslostduring "ltration (1992}1993), and Trichodesmium abundance (1995}1996) were performed at the BATS site. The BATS site shows striking seasonal patterns in hydrography and phytoplankton primary productivity, with a strong maximumimmediatelyfollowingthedeepwintermixingofthewatercolumn.Followingthepeakinprimary production,bacterialabundanceshowedonlyslightlyelevatedlevelsinspring.MaximaofChl-a andPOC also were associated with the primary production peaks, but these particle concentrations became less pronounced through summer and fall. An average of 26% of total POC collected in Niskin water bottles settled below the spigot before it could be sampled. An average of 47% of all bacterial cells passed the nominalporesizeofaWhatmanGF/F "lter, and total POC measurements generated from GF/F "ltered seawatersampleshadtobecorrectedforthisloss.TheaverageintegratedstocksoftotalPOCintheupper 65mofthewatercolumnwas32%pigmentedphytoplankton,15%microheterotrophs,54%otherdetrital matter (32:15:54). Phytoplankton C equaled bacterial C in the 65}135m depth range (16:19:65), but phytoplanktonCwasvirtuallynon-existentdeeperthan135m(2:14:74).BacterialCbiomasswashigher than phytoplankton in surface waters outside the spring bloom period, but carbon not accounted for by 0967-0645/01/$-see front matter  2001 Elsevier Science Ltd. All rights reserved. PII:S0967-0645(00)00156-9