Summary of Abstract Submission

Abstract Submission No. IO50-07-0086PresentationPoster


K. Banse *1, J.A. Rudyakov 2, S.W.A. Naqvi3, A. Vereshchaka4, F. Pollehne5, J.R.:Postel1

1 Oceanography, Univ. of Washington, USA
2 formerly Shirshov Inst. Okeanol, Russia
3 CSIR Inst. Oceanography, India
4 Shirshov Inst. Okeanol. Akad. Nauk, Russia
5 Inst. Baltic Research , Germany


In the Oxygen Minimum Zone (OMZ) of the Arabian Sea in 1959 a minimum of net-collected zooplankton was observed in 1959. Also, in the early 2010s in the Secondary Nitrite Maximum (SNM) of the OMZs of the eastern equatorial South and North Pacific, NO2- from NO3- reduction was recorded only at < 50 nM of dissolved O2 (as measured by the new STOX electrode), well below the limit of the Winkler titration. So, at depth, NO2- concentration exceeding 0.5 ÁM could be taken as a reliable indicator for this condition, applicable also to historical NO2- data from OMZs worldwide. The SNM is now considered as ?functionally anoxic? for metazoans and thus excludes growth and maintenance of copepod populations. We report counts of small copepods (< 2 mm length, mostly < 1.5 mm) sampled in 1978 with 120-Liter bottles in daytime on 6 stations off Peru near 15oS. Seasonal upwelling had drawn the SNM partially onto the shelf with up to 8 ÁM NO2-. Aside from stray specimens and large diel migrants, small species were indeed absent at > 0.5 ÁM NO2-. Concurrent closely-spaced net hauls, though, contained small copepods, as is true in SNMs worldwide, where only metazoan minima but not absence is found. --- Thus, are net hauls invariably somewhat contaminated, and collection together with NO2- by, say, 30-Liter Niskin bottles is the solution, or does occurrence of O2 in pockets within the OMZ permits aerobic populations to persist in SNMs? Small-scale distribution, however, is difficult to study by point samples from bottles or pumps.