GATEWAY CLOSURES AND OCEAN CIRCULATION DURING THE LATE MIOCENE (~13-5 MA)

Long-term climate change is driven by tectonic influences, including the closing of ocean gateways. The middle to late Miocene (~13-5 Ma) witnessed the reorganization of both tropical ocean circulation and deep water production due to the increasing constriction of the Indonesian and Central American seaways. For example, today the waters of the Pacific equatorial current system do not move freely into the Indian Ocean (i.e., via the Indonesian Throughflow, ITF) but instead pile up to form the Western Pacific Warm Pool (a thermal anomaly that greatly influences tropical Pacific climate and ocean circulation). However, we show that during middle to late Miocene time, progressive restriction of the ITF, modulated by sea level fluctuations, resulted in the waxing and waning of a proto-warm pool in the western equatorial Pacific (WEP). The proto-warm pool profoundly affected the early late Miocene “carbonate crash” (an anomalous decrease of carbonate in deep sea sediments) and the late Miocene “biogenic bloom” (sharp increase in carbonate accumulation rates across the tropical Indo-Pacific).

We hypothesize that El Niño/La Niña-like alternations of tropical carbonate preservation and productivity between the western and eastern equatorial Pacific during the late Miocene were the consequence of early warm pool development and decay. A proto-warm pool was formed ~12.1-10.6 Ma, which initiated a nutrient-rich Equatorial Undercurrent and/or increased Trade Wind strength. These La Niña-like conditions sustained carbonate productivity in the eastern equatorial Pacific at a time when carbonate preservation sharply declined in the Caribbean. Proto-warm pool weakening and El Niño-like conditions ~10.6-9.5 Ma intensified a “carbonate crash” in the EEP, while resurgence of the warm pool and La Niña-like conditions after ~6.5 Ma spurred a “biogenic bloom”. The production of deep water in the northern North Atlantic (i.e., Northern Component Water, NCW) may also have been modulated by sea level fluctuations as the Central American Seaway became increasingly constricted by the uplift of the Panama sill. We argue that the sea level fluctuations that facilitated the early development of a proto-warm pool in the WEP, particularly the Mi5 event at 11.4 Ma, also controlled NCW production in the North Atlantic.