The number 14 of the process carbon 14 dating denotes
The number 14 of the process carbon 14 dating denotes - Free Online
The most obvious driver of warmth during the MCO would be higher CO record is presented that, in contrast to this long standing view, shows a remarkable agreement with indicators of the thermal state of the Earth System during the middle Miocene, for instance, the oxygen isotopic composition of benthic foraminifera (which reflect ice volume and bottom water temperature) and the state of the Antarctic Ice Sheet (Figure 1).
) and the Antarctic Ice Sheet (AIS) retreated behind the current ice margin at this time. This of course has potentially worrying consequences for our future as we approach Miocene-like CO dropped to lower than pre-industrial values (280 ppm; Figure 1), the Miocene is thought to be significantly warmer than the pre-industrial. In particular, several studies (including this recent one in Nature) indicate that climate cooled from the Late Miocene to the Pliocene (11 to 2.5 million years ago) – and if CO) reconstructed at ODP 761 (Lear et al., 2010) – this parameter is just ice-volume. Cenozoic benthic foraminiferal Mg/Ca and Li/Ca records: Toward unlocking temperatures and saturation states. (d) schematic summary of shore based reconstructions of the Antarctic Ice Sheet with the length of the black bands incorporating both dating uncertainties and the likely duration of events (Sugden and Denton, 2004; Rocchi et al., 2006; Lewis et al., 2006; Lewis et al., 2007; Lewis et al., 2008), (e) AIS size based on heavy mineral assemblage in the AND-2A drill hole, Ross Sea (Hauptvogel and Passhier, 2012), (f) accumulation rate of debris delivered to the North Atlantic by ice bergs (ice rafted debris; IRD) 0.5 mm in size (from Winkler et al., 2002) and (g) schematic Antarctic glacial history based on the results from the AND-2A drill hole, Ross Sea (Passchier et al., 2011). Our new data suggests that it did this at a similar level of CO (~350-400 ppm) to that associated with its regrowth at the end of the MCO (Figure 1). According to ice sheet models this shouldn’t happen, because the AIS is so cold, bright and elevated, that a higher CO (and hence more warmth) is required to melt it than is required to form it in the first place (a process known as hysteresis).
The answer to this conundrum is that it is likely some portion of the AIS is more mobile than the models are able to simulate (e.g.
those portions, such as the Aurora subglacial basin, currently below sea-level, see
by Gavin Foster, Carrie Lear and James Rae The Miocene epoch spans a relatively long period of Earth’s history from 5 million to 23 million years ago.
It contains the middle Miocene Climatic Optimum (from around 17 to 15 million years ago, also known as the MCO for short) – a period of global warmth (perhaps as much as 4-5 C warmer than today) punctuating the overall cooling trend that has characterised the last 50 million years. Mid-Miocene cooling and the extinction of tundra in continental Antarctica.
Notably, the MCO is associated with (amongst other things) a smaller than modern Antarctic Ice Sheet. Proceedings of the National Academy of Science 105, 10676-10680.
This is therefore a very useful period to study as it may serve as an analogue for our warm future, or at the very least, as a vital guide to how the Earth system functions when it’s warmer than today.