The article for this week is:
Bohaty, Steven M. and James C. Zachos. 2003. Significant Southern Ocean warming event in the late middle Eocene. Geology 31:1017-1020.
As you're reading this paper, try to keep the QuALMRI format in mind. What is the question for this paper? What inferences does it make? etc. Some other questions to think about are:
What important assumption is made in the oxygen isotope analysis of this paper? Do you think it's appropriate?
This paper includes an analysis of carbon isotopes, which we haven't talked about yet. Why do you think these researchers were interested in carbon isotopes? What did they learn from them?
What implications does this study have for the climate change event we are currently experiencing?
What research would you like to do to evaluate the results of this study?
Ruddiman: Found the report summarizing foramifers shellsdecrease by 1% for each 4.2 C degree increase in ocean temperature; if seawater cools, 18O values become heavier; changes in size of ice sheets also alter 18O in shells;Ratio of Mc and Ca in foraminifera used as index; Mg substitutes for Ca depending on temperature of water, all of which should be compared to: shells decrease by 1% for each 4.2 C degree increase in ocean temperature; if seawater cools, 18O values become heavier; changes in size of ice sheets also alter 18O in shells, and fractionation...was interesting and so well written it was easy to understand, but a graph should would help...
ReplyDeleteIn the article by Bohaty et al. (2003) this week, the main question was if δO18 values correlated with higher than normal δC13 values which represented a rise in global average temperature at the Eocene/ Oligocene boundary. The main assumption is that carbon drove this change and that it is not a symptom of this change. The assumption about oxygen is that this rise in δO18 is a result of warming on climate and that it is not a result of increased plant life which also favors increase of δO18 in the atmosphere. It seems like more study of plant life and other events is needed to fully understand the oxygen isotope ratios, preferably with known atmospheric levels in a laboratory setting. This paper examines carbon in an attempt to explain the climactic shift at this boundary. They learned that a correlation exists between heavy carbon and oxygen isotopes at this time period and that the heavy isotopes were rich in the strata examined. It suggests that the climate change happening now is a result of increased CO2. It would be interesting to know whether CO2 preferentially attaches as heavy isotopes. I would also like to know corresponding methane values in order to validate this study’s findings since that is what it is trying to prove is not the cause of the climate change.
ReplyDeleteInferences about the cause(s) of the middle Eocene warming rule out methane hydrate dissociation and instead point toward metamorphic decarbonation or volcanism. Makes sense, given that methane is a more effective greenhouse gas than CO2 and may have led to a positive feedback resulting in a prolonged negative d13C / warming period as in the 55 mya Paleocene-Eocene warming.
ReplyDeleteI didn't know anything about methane hydrate before this paper, but after some investigation, its role in climate change seems worthy of attention. Here's an interesting abstract that includes some NM scientists:
http://www.agu.org/pubs/crossref/2011/2011JC007189.shtml
Metta RavenHeart. Feb 15, 2012.
ReplyDeleteSouthern Ocean Temperatures are interpreted for the middle Eocene period by analyzing dO-18 records of temperature variations and sea water composition. Assumptions are made regarding ice volume as a primary constraint for the interpretation of the meaning of dO-18 levels. The greatest emphasis in interpreting temperature flucttuations is given to Oxygen isotopes from various sources. The addition of various types of Carbon level data helps to corroborate the interpretations and I think is almost equally important because it gives further insight into possible causes of warming. Most plausible for me is the effect of sea floor spreading and consequent volcanism and metamorphism in the Himalayan orogeny, plus changes in sea currents. The greatest impact from methane would probably have been at the 55 my PETM, so I imagine that might be why they ruled it out a a considerable cause for the mid Eocene warming.
I don't know if other papers have been like this and I just didn't notice, but I appreciate the steps of analysis. Splitting it into Results, interpretation, and significance helped separate the authors' thoughts on the results from the pure data.
ReplyDeleteThis paper could be very relevant to the current situation. It is talking about a short period of time where the climate became much warmer, and, if the paper is to be believed, the mechanism was the same as the current situation, more CO2 in the atmosphere.
The article assumes in it statement that ODP Sites 689, 744, and 748 at ~1500-1800 m water depth; whereas Site 690 and 738 were at ~2000-2500m in the middle to late Eocene. The “Introduction” states: “Currently only one moderate-resolution stable isotope record that spans the middle to late Eocene interval is available from a Southern Ocean site” (ODP site 689). The articles “Results” refers to multiple middle to late Eocene stable isotope records (Fig 2), even though records are not available between 50 and 32 ma.
ReplyDeleteAlso regarding the “Introduction” statement of one stable isotope record. Data for all other sites appear to have been constructed with biostratigraphic and magnetostratigraphic data. Figure 1. shows sites 744, 748 and 738 being on a land mass. Figure 3 shows stable isotope stratigraphy identified at ODP 689, 738 and 748. So, where did the stable isotope data for ODP 738 and 748 come from?
The article’s section “Interpretation” states “an assumption regarding ice volume are required to estimate temperatures.”
I agree with Danika re: the breakdown of the study, and a whisper of hope about our current CO2 situation.
These researchers better get on their seahorses, if they expect to get funding without a sentence or two what their findings might mean to us today.
Collins found a good abstract on methane..thanks!
I think it is important to keep in mind that although in geological context the time period described in this paper is "short", the time frame in regard to anthropogenic CO2 emissions is but a small fraction of the time frame of this study.
ReplyDeleteThis paper also had me trying to remember the details of methane and its reactions in the atmosphere. If I remember correctly methane is a much stronger greenhouse gas, but for a much shorter period (~10yrs). Again if I remember correctly methane reacts with hydroxyl radicals and is converted to carbon dioxide. Which I have heard the argument that due to the short time methane stays in the atmosphere and the fact that it gets converted to carbon dioxide, any focus diverted from carbon dioxide research, understanding and awareness is misguided. And I agree.
Mike J
Overall, I thought that this article was very interesting because it shows all the information we can gain from cores. With a core we can look at identifying things like climate, environment, and what we can expect in our geologic future. I think coring is going to be something that we should really invest in for our understanding of Earth. I mean not only do we gain understanding about our geologic past but also I’m sure coring is often driven by our search for new resources.
ReplyDeleteIn terms of the idea on methane being a larger driver for climate warming I remember reading an article on how methane is trapped in the ocean in ice. Then as warmer ocean temperatures become more prevalent the methane is released which allows a drastic change from cold to warm climates. I believe the article used this as an explanation for the PETM but I’m not positive. Enlighten me if anyone may be familiar with this article.
This article is interesting and I can see how the information gathered here is important for understanding large scale climate change. I can't say I find the study of isotope change terribly riveting, but that's just a personal bias.
ReplyDeleteThe article mentioned that during this time there was an expected drop of global mean temperature of approximately -~6 degrees centigrade, this kind of dramatic global change in temperature must have had dramatic effects on flora and fauna, especially near the changing lines of tundra and taiga environments. I think it would be worth looking at this same time period (If available) in the fossil record of subarctic zones to track changes in animal adaptation to these shifts.