Sink or link? The bacterial role in benthic carbon cycling in the Arabian Sea's oxygen minimum zone
- 1Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research NIOZ-Yerseke Korringaweg 7, 4401CT Yerseke, the Netherlands
- 2International Research Institute of Stavanger (IRIS), Mekjarvik 12, 4070 Randaberg, Norway
- 3Department of Earth Sciences-Geochemistry Faculty of Geosciences, Utrecht University Budapestlaan 4, 3584 CD Utrecht, the Netherlands
Abstract. The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea's oxygen minimum zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the 7 day experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient, in sediments both inside and outside the OMZ. Moreover, metazoans directly consumed labile particulate organic matter resources and thus competed with bacteria for phytodetritus.