Short term patterns of vertical particle flux in the northen Benguela upwelling: a comparison between sinking POC and respiratory carbon consumption

From Sediment Traps • Plankton Ecophysiology Group , Instituto de Oceanografía y Cambio Global, ULPGC , 35017 , Canary Islands , Spain. ' Zooplankton Ecology Group , Baltie Sea Research Institute , 0· 18 1 19 Rostoek , Wamemünde , Germany . INTRODUCTION Both 1055 01 material lrom the water column and gain to the sediment are important proeesses in marine ecology and biogeochemistry , as the transport balance between water and sediment controls quantity and quality 01 marine lile. Upwelling systems , as hotspot 01 marine productivity , are particularly interesting in this coneern . Here , we have studied the short term variability 01 vertieel caribon flux on the Namibian shell by two altemative approaches: R8Iplratlon allociated e flux modela (Fe) , whi ch are based on modeling the respiratory organic caribon consumption in the water column , by the integration 01 vertical profiles 01 the respiratory electron transport system (ETS) . Second, automatic aedlment trapa (STa) that were succesively moored and that collected sinking material with daily sampling periods. Temporal variability was stronger than the effect 01 distanee between stations. Thus , high respiration rates in the water column as well as high particle export rates were attributed to filaments 01 upwelling water arising from the south , while lower rates were associated with more oligotrophic waters . Therelore , in order to compare both approaches , !hese two distinct situations were considered . Location & Seawater characteristics Fl u xes 01 all varia b les dls tingu is hed two sedimentation states at the two sta tion s: a hlgh· •• d period t hat was ma i nly dominated by diatoms , and a low · •• d perlod w her e the ooccolithophoride importanee inereased . NAM006R and NAM0110 d is played similar water eharaeteristie but they were notably different Irom NAM01 1 R, wh l eh was sampled ten ~ day s later . The firs t two were aHributed to cold water fi l aments , while ! the thlrd corresponded to a later temporal stage 01 these waters , ~ ( mgm 4-¡ '"" " NAMooe ~ "" 20~ ...... ":" ' E :" i 000 < " 1 E _ ~;;: ... .. ~ -~ ~~ • ~ o ~~~~'/., .... ~~1!'~ 'fl ~ ~ '\~ "' fI'P'/.~,,/~ .~ b ,¡P,,~ Moonng days DW __ PON POP -. POC .o. PSI I o 2 " , • '0 12 \. It " lO o ~' ,oo l: ~~ .. Flg. 2. Deplll • profilo. of chk>rophy1land S8awater density (sigma·I) . Flg . 1. Croawhelf aection o, Ihe study area al 2005 off Walvil 8. y (Namlbia). Sedimant trapa w.r. moored at 150 m (NAMOO6).oo 320 m (NAM011) . Wa ter coIumn al NAM011 was umpled twk:e . From Water Column Respiration Resp i ration tr e nded parallel at NAM006R and NAM0110 due to both mleroplankton and small zoop l an k ton . In contrast , the surface resp i ration at NAM011 R was dominated by large zooplankton . R o , ( ~moI° t m -l d ! ) Ro , (~O , m -l d l ) Ro, (~moI O, m I d 1) o 50 .00 .00 200 250 lOO O 50 .00 '50 200 250 300 o 50 '00 '50 200 '00 '50 O, ~ 1 O O l' 50 '~: .... .00 9 -"" '00-200"", e roo 200 ~ 200-500"", 200 -"'- 5OC).,OOO ~ ~ ", ' -, ,. 1000"", ... 300 300 ~ NAMooeR NAMO ll D NAMOllR 200 I <DO <DO Flg. 5. Vertical nultes of ma .. ( dry weight , DW) , particulate organ ic nilrogen (PON), pho&ph.t. (POP), .. rboo (POC) and ailica (PSI) . Flg , 3. Respiratory Ol()'gen consumption (R~) depth profiles 01 mlcropla n kton .nd s1ze-frlCtion.ted zoopl.nkton . Comparlson: ST vs Fe Durlng the hlgh·sed period , !he poc flux values Irom STs were higher than those lrom the Fe models , Du ri ng the low·sed period, the Fe value was twice the ST value . This dlserepancy Is explained by diff erences in the plankton oommunity struClure and by their seHling veloc~ies . " NAMOO6R NAM011D _ STs _ Fe NAMOl1R Fig . 6. Compari$OO between STs an<! Fe POC nux values . T.bl, l. Equation parameters 'or the pow8r functlon respiraUon mocIe+ oflhe CO 2 production , R CQlR.l -- (mmol CO 2 d" m -l ), Fe calculallon StIIltoIl R. ,., N ¡I, \! lOO R \ I IC"I\IIMNlkWIl ' 33 "'."" 091 f, 1.. RcQ.dz J Il", 'd, ~ "' .. o 0:,9 =~.+I'J rntAl R co • ,m .()!>.', ... 1/ _. _ n.. '(b+ )111::"+1 SA ~ flIIlD \I ~nktutl "" .()4n o'"' From the R o. profiles (F ig. 3), the R C02 is """"""too am -O I 097 estimated and the best fit tor each profile TlUI Rn .. 1111 -0063 determined (Ta ble 1). Then , definite int egra ls ~A ~ toIlR \Ikroplanktoo 63 .().IoK1 o . ., 01 total R"", are calculated Irom any depth Zoopionh ... 1~T.17 ·)254 Og; be low !he euphotie zone (zJ to the seafloor Tow R ro. .... -0939 (zJ. The resultant carbon flux models (Fe) are shown in F igA . CONCLUSIONS Regardless 01 distance to shore, up welli ng filaments generated two distinet situations : ./ Ouring hlgh · sed period, the predominance 01 dlatoms lormed last sinking partides which yielded higher POC values in the STs than in the respiration based Fe caleulations. ./ The low·sed period , charaClerized by slow sinking partieles , sustained a relatively hig h er water column respiration . Fe values were higher than the values from the STs . O 20 o '00 g 200 ! 300 -+- NAMOO6R -<>- NAM011D 400 NAM011R Flg . 4. Carbon nux models (Fe) al the th ree s ta llons . Aknow/edg.m.nts