Thursday, August 21, 2014

Geology Sonnet 3

Science week geology sonnet number three!  See previous posts for background.

A pox on all those proxies non-unique
Which make interpretation hard to do.
Magnesium to calcium we seek
Sea Temp'rature, and not pCO2.
So lithium, uranium are used
To disambiguate the Mg curve.
O. umbonatus' data's not recused,
Antarctice ice growth isotopes observe.
But whence the melting in the Miocene?
Here isotopes of carbon join our tale,
And sedimentary burndown in marine
Organic carbon makes the icecap fail.
  Antarctic ice was thawed by CO2
  Let's try repeating this effect anew.

Elaine M. Mawbey and Caroline H. Lear. (2013) Carbon cycle feedbacks during the Oligocene-Miocene transient glaciation. Geology 41. 963-966.


Ice sheet models suggest that once formed, the large, high-altitude East Antarctic Ice Sheet was relatively self-stabilizing, due to its cold upper surface. The ice sheet hysteresis problem results from an inability to reconcile this expectation with geological evidence for episodes of ice sheet retreat. A classic example of this problem is manifested in benthic foraminiferal oxygen isotope records across the Oligocene-Miocene boundary (ca. 23 Ma), which display a transient ∼1‰ excursion to higher values. The inferred increase and subsequent decrease in ice volume has been linked to advance and retreat of the Antarctic ice sheet across the continental shelf. However, oxygen isotope records alone do not provide unambiguous records of temperature and ice volume, hindering assessment of the driving mechanism for these variations. Here we present new benthic foraminiferal Mg/Ca, Li/Ca, and U/Ca records across the Oligocene-Miocene boundary from Ocean Drilling Program Sites 926 and 929. Our records demonstrate that Atlantic bottom-water temperatures varied cyclically, with the main cooling and warming steps followed by ice growth and decay respectively. We suggest that enhanced organic carbon burial acted as a positive feedback as climate cooled. Several lines of evidence suggest that the deglaciation was associated with an input of carbon to the ocean-atmosphere system, culminating in a previously unidentified seafloor dissolution event. We suggest that one of the initial sources of carbon was organic matter oxidation in ocean sediments. This study demonstrates that carbon cycle feedbacks should be considered when evaluating the stability of ancient ice sheets.

Other geosonnets: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63

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