The Latest Miocene–Early Pliocene biogenic bloom: a revised Indian Ocean perspective

Abstract

Numerous investigations of Neogene sediment sequences from the Indian and Pacific Oceans have led to a paleoceanographic hypothesis that recently has been coined the “biogenic bloom”. This hypothesis suggests that primary productivity increased substantially at Indo-Pacific upwelling zones during the Latest Miocene–Early Pliocene. Although it is clear that recognition of a widespread biogenic bloom provides a fundamental framework for understanding Late Neogene global change, it also is apparent that investigations of this phenomena require syntheses of a variety of information from time-correlated sediment sequences that span large oceanic regions. Late Neogene polarity chron boundaries and nannofossil events are placed on a common and current time scale for 12 Ocean Drilling Program (ODP) sediment sequences in order to construct a coherent description of the biogenic bloom in the Indian Ocean. Carbonate mass accumulation rates (MARs) were significantly higher than present-day in the north and west Indian Ocean between 9.0 and 3.5 Ma. Sediment deposited during this time interval also is dominated by planktic faunal assemblages that are indicative of high-productivity, and redox conditions that are explained by an increase in the supply of organic carbon. Further, sediment of this age contains benthic faunal assemblages and chemical characteristics that are consistent with low dissolved O 2 in intermediate waters. These observations collectively suggest that, between 9.0 and 3.5 Ma, productivity in the north and west Indian Ocean was significantly higher than present-day, and the intermediate water oxygen minimum zone (OMZ) was more extensive than present-day. This paleoceanographic condition was most intense between 6.0 and 5.0 Ma in the Indian Ocean. Comparison of the Indian Ocean sites with two locations in the Pacific Ocean suggests that the biogenic bloom was time-coincident in the Indian and Pacific Oceans. The biogenic bloom, therefore, implies an important change in global nutrient cycling occurred during the Latest Miocene–Early Pliocene, although a satisfactory explanation for the change remains elusive.