A mechanism for freshening the Caribbean Sea in pre‐Ice Age time

Abstract

Many believe that the Central American Seaway closed near 4 Ma and that that closure led to increased salinity in the Caribbean Sea and stronger Meridional Overturning Circulation in the Atlantic, which facilitated the waxing and waning of ice sheets in the Northern Hemisphere. We offer an alternative explanation for Caribbean salinification. The atmosphere transports approximately 0.23 Sv (1 Sv = 10 6 m 3 s À1 )of fresh water (moisture) from the Caribbean to the Pacific today, but that amount varies by >20% during El Niño-Southern Oscillation events. Regressions of moisture transport against the Niño-3 index, a measure of the sea surface temperature in the eastern tropical Pacific, show less moisture transport from the Caribbean during El Niño events than average. Abundant evidence indicates that at 3-4 Ma the eastern tropical Pacific was 3.5-4°C warmer than today, and if so, an extrapolation of such regressions suggests that smaller moisture transport across Central America might account for paleoceanographic inferences of a smaller salinity difference between the Caribbean and Pacific at that time. Accordingly, that decreased salinity difference at~3-4 Ma would not require blockage of relatively fresh Pacific water at~2-4 Ma by the closure of the Central American Seaway, but rather would be consistent with a transition from El Niño to La Niña-like conditions in the eastern tropical Pacific around that time.

Comment (1) on “Formation of the Isthmus of Panama” by O’Dea et al .

“…Some of these links have been criticized or dismissed [for example, ( 4 , 25 , 33 )] and are still far from being resolved. Unfortunately, O’Dea et al .…”

Low‐frequency Pliocene climate variability in the eastern Nordic Seas

“…The Caribbean and North Atlantic became gradually warmer and saltier from circa 4.6 Ma, enhancing the AMOC [ Haug and Tiedemann , ; Sarnthein et al ., ] (Figure ), although the exact mechanism behind the enhanced AMOC is still discussed [ Haug and Tiedemann , ; Lunt et al ., ; Mestas‐Nunez and Molnar , ; Sarnthein et al ., ]. Regardless of the underlying driver, an intensified AMOC from circa 4.6 Ma would have brought warmer and saltier water to the North Atlantic, leading to a more evaporative high‐latitude ocean and consequently increased salinities.…”

Atlantic Deep-water Response to the Early Pliocene Shoaling of the Central American Seaway

“…Elucidating the timing and nature of the CAS closure is crucial for evaluating its impact on AMOC and climate. However, geological records reveal it as a complex process, with many details remaining unclear and contested 11 12 13 14 15 16 . The timeline of closure events is estimated to range from the emergence of land in the CAS as early as ~15–20 Ma 17 18 , to closure of the deep-water connection by ~7–10 Ma 19 20 , and complete restriction of Pacific-Caribbean surface-water exchange between ~3.5–2.5 Ma 12 .…”

“…Haug and Tiedemann 3 suggested that this interval reflects a major phase in the final closure of the seaway, with shoaling to within 100 m water depth by 4.2 Ma. More recently, however, Mestas-Nuñez and Molnar 13 have suggested that these changes in the Caribbean may be unrelated to CAS shoaling: Instead, they propose it may be a consequence of a shifting dominance of El Niño- to La Niña-like conditions in the eastern tropical Pacific. Regardless of the cause, the build-up of heat and salinity in Caribbean surface waters during the period ~4.7–4.2 Ma is uncontested and, as a consequence, the expectation of an increase in AMOC remains.…”