A One-box Ocean Chamber Model Explores the Differences in Ocean Pumping During the Last Glacial Maximum and the modern/Holocene using a Delta-O-18 Tracer

Abstract:

Scientists are interested in the shifts in ocean pumping rates from Last Glacial Maximum (LGM) to the the modern/Holocene in part because of the imperative of healing climate change in the modern era; ocean tracers such as delta-O-18 can be used in simple models to diagnose the changes in circulation between disparate eras. If the ocean pumping works similarly in stable but different climate regimes, then we can adjust the flux of atmospheric vapor transport and/or overturning circulation into and out of its chambers, and generate appropriate concentration changes in delta-O-18.

Here a single model chamber represents the North Atlantic ocean, which is an important site of deep water formation and the recipient of freshwater transport from vapor from the mid-latitudes and runoff from the high-latitudes. Ocean flux from the low-latitude surface and the deep ocean are assumed to be constant (stable) during the climate eras explored. One algebraic expression solves the tracer concentration in the surface North Atlantic. Differing flux values for the overturning, vapor transport, and runoff are explored in the modern/Holocene and LGM.

It is possible to recreate the high-latitude Atlantic surface ocean tracer concentration during the modern/Holocene using literature values of overturning, river runoff, and complex model estimates of vapor transport into the high latitudes. Likewise, estimates of high-latitude surface ocean delta-O-18 during the LGM can be established by slowing vertical mixing with the deep ocean and river runoff with the surface ocean, and maintaining a similar overturning circulation as in the modern/Holocene.

Finally, implications for the use of a simple yet evolving pump system between the LGM and the Holocene are discussed for modelling the shifts in tracer concentrations in the low-latitude surface and deep ocean between each of these stable climate regimes.