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Proposed Changes for MIS 11

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chose to expand on the article for Marine Isotope Stage 11 (MIS 11) to include sections for potential causes and why it is currently considered an analog for Holocene climate. The current article for MIS 11 mentions in the lede that there there may be some correlation between climatic elements of MIS 11 and the Holocene, but there is no exploration of why that is. Additionally, the article focuses on what we know of climate characteristics from proxy records, but does not discuss the lead in processes or what might have caused MIS 11 to last longer than most other interglacial periods in the climate record. I might begin by discussing those climate elements (ice volume, ocean temperature, etc) that are known to be similar and what proxies tell us that[1]. Next I would add a discussion of why MIS 11 is theorized to be an analog for the future Holocene/Anthropocene climatic trend[2][3] and how our observation of this period in the past can help us model predictions for the future[4]. Finally, I would consider changing or elaborating on this lede, particularly to address the comparison of MIS 5 to MIS 11 which I have not been able to find any evidence for yet. This will require more research but it may be erroneous or outdated information.

Outline for Marine Isotope Stage 11 (5/11/17)

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I will primarily be surveying the literature concerning the comparison of climatic conditions during Marine Isotope Stage 11 (MIS 11) approximately 420 thousand years ago to those of the Holocene. The MIS 11 has been regarded as a representing a good comparison to the Holocene in regards to the orbital forcing conditions in the millenial-scale precessional cycle[5]. Oxygen isotope ratios for MIS 11 are similar to those of the Holocene, suggesting some to conclude that sea level, ice sheet extent, ocean temperature and salinity may have been very similar to the Holocene[6].

Holocene Analog

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Due to similarities in the oxygen isotope records of MIS 11 and the Holocene, many have theorized that the conditions of MIS 11, which led to a longer than usual interglacial period (~27,000 years as opposed to ~10,000 years), are an indicator of future Holocene long term climate conditions[1]. It is believed that insolation rates related to the precessional cycle now and then are roughly equivalent. MIS 11 is unique in that it occurred over the span of two orbital maxima, while all other marine isotope stages have lasted only one. This is explained by a weak minimum between the two maxima resulting in less pronounced climate change and avoiding another glacial period[1]. I believe that replicating a few charts could really help explain this latter point.

Dissimilarities

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There are some alternate hypotheses that challenge the comparison of MIS 11 to the Holocene based on some newer, high-resolution data becoming available. It is widely believed that sea level was anywhere from 13-20 meters higher during MIS 11 than today, indicating that Antarctica and Greenland had become at least partially deglaciated[7]. This theory has been challenged by evidence that suggests sea level was closer to today's levels, and possibly no more than ~6 meters higher[8]. Similarly, there is disagreement that MIS 11 is actually the best historical proxy for the Holocene. It has been proposed that MIS 19 is actually more representative of the insolation conditions characteristic of the Holocene, and that the two-peak thermal maxima of MIS 11 makes it unique[9].

Things to Improve in This Article

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I believe that some of the concepts in this article are poorly cited and could use stronger explanation. Additionally, there are a few places in which one side of a theoretical debate is presented without acknowledging the other. Specifically, some of the information about sea level and climatic similarities could be expanded to include the another perspective. The article as a whole is somewhat arbitrarily organized, but short of redoing the whole thing I would add the two sections above (Holocene Analog and Dissimilarities) and greatly expand on the Characteristics section to include much more detail about all the elements of MIS 11 that are said to resemble today's climate. Dtolson1 (talk) 05:28, 12 May 2017 (UTC)

Article in Progress

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Approximate temporal locations of MIS 11 and the Mid-Brunhes Event relative to dust, CO2 and ocean temperature

Marine Isotope Stage 11 or MIS 11 is a Marine Isotope Stage in the geologic temperature record, covering the interglacial period between 424,000 and 374,000 years ago.[10] It corresponds to the geological Hoxnian Stage. MIS 11 is distinct from other interglacial periods in that it lasted considerably longer than others. It is believed that sea level was higher and ice sheet extent was lower than it is presently, though to what extent is being debated. At roughly the onset of MIS 11 was the Mid-Brunhes Event, a period of increased carbonate dissolution to the ocean. MIS 1 (the Holocene) and MIS 11 share some characteristics in common, leading some to consider MIS 11 as a useful analog for modeling future climate change.

Significance

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Mid-Bruhnes Event

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The Mid-Brunhes Event (MBE) is a time period that roughly corresponds to 'Termination V' between MIS 12 and MIS 11. Centered on MIS 11, this was a period of increased carbonate dissolution into the oceans that roughly corresponds to a transition in 100,000 year climatic cycles from low to high amplitude. This observation sits in contrast to atmospheric CO2 levels that were roughly equivalent to atmospheric CO2 in the early Holocene[11]. Cronin concludes that the high dissolution of carbonate in the oceans during the MBE has several competing explanations and is currently not fully understood[11].

Abnormally Long Interglacial Period

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MIS 11 is characterized by overall warm sea-surface temperatures in high latitudes, strong thermohaline circulation, unusual blooms of calcareous plankton in high latitudes, higher sea level than the present, coral reef expansion resulting in enlarged accumulation of neritic carbonates, and overall poor pelagic carbonate preservation and strong dissolution in certain areas. MIS 11 is considered the warmest interglacial period of the last 500,000 years[12].

On the other hand, the conclusion that MIS 11 was significantly warmer than the Holocene has been called into question by some. Hodell et al. argue that low temporal resolution of proxy records combined with the unusually long duration of MIS 11 may result in erroneous amplitude readings[13]. This conclusion caused Hodell to revise their previously reported findings (1993) of high temperatures after analyzing ice core proxies with higher temporal resolutions[13][14].

The duration of MIS 11 is considered to have been much longer than other interglacials in the climate record. Whereas most interglacial periods are understood to last ~10,000 years on average, scientists conclude that warm sea temperatures of MIS 11 lasted up to 30,000 years[15][16][11]. This understanding is based on the effects of a 400,000-year orbital eccentricity/precession cycle that causes diminished variability in summer insolation rates (see chart above). Hodell et al. cite the combination of eccentricity and precession lows that led to fewer cold substages of MIS 11, substages which were much stronger when eccentricity and precession variables were stronger in the later Marine Isotope Stages[5].

Characteristics

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Concentration of CO2

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Carbon dioxide concentration during MIS 11 was possibly similar to that documented in the pre-industrial period, but not especially high when compared to other interglacial periods (for example, CO2 concentration was probably higher during MIS 9.[17] In addition, a peculiar feature of MIS 11 is that an early CO2 peak, usually associated to the deglaciation in response to increasing temperatures, is not detected.

Seemingly, the long-lasting interglacial conditions that are documented during MIS 11 depend on the peculiar interplay between CO2 concentration and insolation. In fact, during periods of both eccentricity and precession minima, even small variations in total insolation might lead the control of climate to greenhouse gasses, in particular CO2.

Carbonate productivity

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5 million year history, representing the Lisiecki and Raymo (2005) LR04 Benthic Stack

In shallow-water environments, the development of several major reef systems (such as the Great Barrier Reef) accompanied increased reef carbonate production. Calcium carbonate production peaked in subpolar and subtropical oceans, reflecting a shift in plankton ecology from diatoms to calcareous plankton due to changes in seawater temperatures, which were apparently warmer at low latitudes. The increased production of carbonate in either continental shelves and mid-latitude open-ocean environments may partly explain the high rates of carbonate sediments dissolution during MIS 11 throughout ocean basins, such as the Indian and Pacific. Indeed, increases in regional carbonate productivity can be only explained by increased carbonate dissolution in other (source) areas. Another explanation for the presence of barrier-reef tracts at low latitudes during MIS 11 is that tropical continental shelves were (at least partly) flooded in response to a major marine transgression (see below).

Sea level & marine transgression

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Beach deposits in Alaska, Bermuda and the Bahamas, as well as uplifted reef terraces in Indonesia, suggest that global sea level reached as much as twenty metres above the present.[18][19][20] δ18
O records show isotopic depletions that are consistent with a sea-level highstand, but temperature effect cannot be confidently disentangled from glacioeustasy. Moreover, the collapse of at least one major ice sheet has to be inferred in order to produce similar high sea-levels, nevertheless, the stability of these ice sheets is one of the main questions in climate-change research: in fact, controversial geologic evidences suggest that present-day polar ice sheets might have been disrupted (or drastically shrunk) during previous Pleistocene interglacials.

The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that both the West Antarctica and the Greenland ice sheets were absent, or at least greatly reduced, during MIS 11. Sedimentary deposits from Greenland suggest a near-complete deglaciation of south Greenland, and a subsequent sea level rise of 4.5 to 6  metres of sea-level-equivalent volume during MIS 11, around 410,000 to 400,000  years ago.[21]

Recent studies using uplift correction techniques suggest that a sea level 20 meters above present was unlikely during MIS 11. By dating uplifted beach sites from MIS 5.5 and using an uplift correction formula developed by Pillans et al.[22], Bowen determined that MIS 11 sea levels could have only been up to six meters higher than present, a finding that calls into question the argument supporting West Antarctic Ice Sheet collapse and major Greenland ice sheet melting in the interglacial period.[23][24]

Astronomical features

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400 ky orbital eccentricity 'lows' corresponding to MIS 1 and MIS 11

In contrast to most other interglacials of the late Quaternary, MIS 11 cannot be straightforwardly explained and modeled solely within the context of Milankovitch forcing mechanisms.[25] The sustained interglacial warmth may have lasted as long as it did, because orbital eccentricity was low and the amplitude of the precessional cycle diminished, resulting in several fewer cold substages during this period and perhaps also induced abrupt climate change at MIS 12–11 transition, the most intense of the past 500 kyrs.

It is notable that MIS 11 developed just after one of the most “heavy” Pleistocene δ18
O glacials (MIS 12). According to some authors, MIS 12 is likely to represent a “minimum” within the 400-kyr cyclicity (which is apparently “stretched” into ca. 500-kyr cycles in the Pleistocene), same as the MIS 24/MIS 22 complex (ca. 900 ka)[26]. In support of this inference is the observation that these dramatic glacial intervals are coincident with periods of major climate reorganization, namely the “Mid-Brunhes Event”[27] and the “Mid-Pleistocene Revolution”[28], respectively.

In view of its pattern of astronomically-driven insolation, MIS 11 may be the best analogue for the near future insolation situation. A 2-D Northern Hemisphere climate model used to simulate climate evolution over MIS 11, MIS 5 and into the future implied that the climatic features and length of MIS 11 may be comparable to the present-future interglacial in the absence of anthropogenic forcing. This consideration has led some authors to the conclusion that the current interglacial period (begun 10 kyr) would have continued for approximately 20–25 kyrs even in the absence of anthropogenic forcing.

MIS 11 as Holocene Analog

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Climate analogs are useful because they allow scientists to test models against known climate variables from known variables, like CO2 levels or orbital forcing cycles, and observed outcomes. Interest in MIS 11 in this regard stems from the hypothesis that the Holocene, in the absence of human-introduced greenhouse gasses, would likely last as long as MIS 11 had[5].

Due to similarities in the oxygen isotope records of MIS 11 and the Holocene, many have theorized that the conditions of MIS 11, which led to a longer than usual interglacial period (~27,000 years as opposed to ~10,000 years), are an indicator of future Holocene long term climate conditions[1]. It is believed that insolation rates related to the precessional cycle now and then are roughly equivalent. MIS 11 is unique in that it occurred over the span of two orbital maxima, while all other marine isotope stages have lasted only one[2]. This is explained by a weak minimum between the two maxima resulting in less pronounced climate change and avoiding another glacial period[1]. Rohling points to the need for identifying low-variability marine isotope stages that only span a single solar maximum, suggesting MIS 19 as a potential candidate[2].

There are some alternate hypotheses that challenge the comparison of MIS 11 to the Holocene based on some newer, high-resolution data becoming available. It is widely believed that sea level was anywhere from 13-20 meters higher during MIS 11 than today, indicating that Antarctica and Greenland had become at least partially deglaciated[7]. This theory has been challenged by evidence that suggests sea level was closer to today's levels, and possibly no more than ~6 meters higher[8]. Similarly, there is disagreement that MIS 11 is actually the best historical proxy for the Holocene. It has been proposed that MIS 19 is actually more representative of the insolation conditions characteristic of the Holocene, and that the two-peak insolation maxima of MIS 11 makes it unique[9].

Ruddiman, in support of his Early Anthropocene hypothesis, rejects the theory that MIS 11 is a good analog for the Holocene. He specifically rejects the conclusion that, absent anthropogenic forcing, the Holocene would have lasted much longer than the more common ~10,000 years due to the combination of orbital forcing mechanisms of the 400,000 year eccentricity cycle[29]. Instead, Ruddiman argues that previous studies arguing MIS1/MIS 11 similarities suffer from misalignment of past and present insolation cycles. He critiques an alignment of EPICA ice core data with modern observations by Broecker and Stocker[30] to make the case that MIS 11 insolation maximum was erroneously aligned with modern summer insolation[31].

Some researchers contend that there is actually some significant differences between the orbital forcing mechanisms of MIS 1 and MIS 11 despite their apparent similarities. Rohling et al. argue that MIS 11 was unique in that the interglacial period corresponded with two relatively weak insolation maxima as opposed to the single insolation maximum of the Holocene. The long duration of MIS 11 can be explained as an abnormally slow deglaciation due to weak variation in insolation over the first minimum-maximum cycle. Rohling et al. conclude that the once the ice-volume minimum and sea-level highstand of MIS 11 were reached - actual interglacial conditions - the period of warmth lasted a more expected ~10,000 years instead of an anomalous 20,000 - 30,000 years[32].

See also

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References

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  1. ^ a b c d e Mcmanus, Jerry; Oppo, Delia; Cullen, James; Healey, Stephanie (2003-01-01). W.oxler, André; Poore, Richard Z.; Burckle, Lloyd H. (eds.). Earth's Climate and Orbital Eccentricity: The Marine Isotope Stage 11 Question. American Geophysical Union. pp. 69–85. doi:10.1029/137gm06/summary. ISBN 9781118668498.
  2. ^ a b c Rohling, E. J.; Braun, K.; Grant, K.; Kucera, M.; Roberts, A. P.; Siddall, M.; Trommer, G. (2010-03-01). "Comparison between Holocene and Marine Isotope Stage-11 sea-level histories". Earth and Planetary Science Letters. 291 (1–4): 97–105. doi:10.1016/j.epsl.2009.12.054.
  3. ^ Tzedakis, P. (Spring 2017). "The MIS 11 – MIS 1 analogy, southern European vegetation, atmospheric methane and the "early anthropogenic hypothesis"" (PDF). Climate of the Past. 6: 131–144.
  4. ^ Loutre, M. F. (2003-07-15). "Clues from MIS 11 to predict the future climate – a modelling point of view". Earth and Planetary Science Letters. 212 (1–2): 213–224. doi:10.1016/S0012-821X(03)00235-8.
  5. ^ a b c Hodell, David A.; Charles, Christopher D.; Ninnemann, Ulysses S. (2000-02-01). "Comparison of interglacial stages in the South Atlantic sector of the southern ocean for the past 450 kyr: implifications for Marine Isotope Stage (MIS) 11". Global and Planetary Change. 24 (1): 7–26. doi:10.1016/S0921-8181(99)00069-7.
  6. ^ McManus, Jerry; Oppo, Delia; Cullen, James; Healey, Stephanie (2003-01-01). "Marine Isotope Stage 11 (MIS 11): Analog for Holocene and future climate?". Washington DC American Geophysical Union Geophysical Monograph Series. 137: 69–85. doi:10.1029/137GM06.
  7. ^ a b Hodell, David A.; Charles, Christopher D.; Ninnemann, Ulysses S. (2000-02-01). "Comparison of interglacial stages in the South Atlantic sector of the southern ocean for the past 450 kyr: implifications for Marine Isotope Stage (MIS) 11". Global and Planetary Change. 24 (1): 7–26. doi:10.1016/S0921-8181(99)00069-7.
  8. ^ a b Bowen, D. (2010). "Sea level ∼400 000 years ago (MIS 11): analogue for present and future sea-level?". Climate of the Past. 6: 19–29.
  9. ^ a b Rohling, E. J.; Braun, K.; Grant, K.; Kucera, M.; Roberts, A. P.; Siddall, M.; Trommer, G. (2010-03-01). "Comparison between Holocene and Marine Isotope Stage-11 sea-level histories". Earth and Planetary Science Letters. 291 (1–4): 97–105. doi:10.1016/j.epsl.2009.12.054.
  10. ^ Lisiecki,Lorraine E.; Raymo, Maureen E. (2005). "A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records". doi:10.1029/2004PA001071.
  11. ^ a b c Cronin, Thomas (2009). Paleoclimates. New York, NY: Columbia University Press. p. 135. ISBN 0231144946.
  12. ^ Howard, W.R. (1997). "A warm future in the past". Nature. 388 (6641): 418–9. doi:10.1038/41201.
  13. ^ a b Hodell, David A.; Charles, Christopher D.; Ninnemann, Ulysses S. (February 2000). "Comparison of interglacial stages in the South Atlantic sector of the southern ocean for the past 450 kyr: implifications for Marine Isotope Stage (MIS) 11". Global and Planetary Change. 24 (1): 7–26. doi:10.1016/S0921-8181(99)00069-7.
  14. ^ Hodell, David A. (1993-02-01). "Late Pleistocene Paleoceanography of the South Atlantic Sector of the Southern Ocean: Ocean Drilling Program Hole 704A". Paleoceanography. 8 (1): 47–67. doi:10.1029/92PA02774. ISSN 1944-9186.
  15. ^ Mcmanus, Jerry; Oppo, Delia; Cullen, James; Healey, Stephanie (2003). W.oxler, André; Poore, Richard Z.; Burckle, Lloyd H. (eds.). Earth's Climate and Orbital Eccentricity: The Marine Isotope Stage 11 Question. American Geophysical Union. pp. 69–85. doi:10.1029/137gm06/summary. ISBN 9781118668498.
  16. ^ Hodell, David A.; Charles, Christopher D.; Ninnemann, Ulysses S. (February 2000). "Comparison of interglacial stages in the South Atlantic sector of the southern ocean for the past 450 kyr: implifications for Marine Isotope Stage (MIS) 11". Global and Planetary Change. 24 (1): 7–26. doi:10.1016/S0921-8181(99)00069-7.
  17. ^ Raynaud, D.; Barnola, J.M.; Souchez, R.; Lorrain, R.; Petit, J.R.; Duval, P.; Lipenkov, V.Y. (July 2005). "Palaeoclimatology: the record for marine isotopic stage 11". Nature. 436 (7047): 39–40. doi:10.1038/43639b. PMID 16001055.
  18. ^ Hearty, P.J.; Kindler, P.; Cheng, H.; Edwards, R.L. (April 1999). "Evidence for a +20 m middle Pleistocene sea-level highstand (Bermuda and Bahamas) and partial collapse of Antarctic ice". Geology. 27 (4): 375–8. doi:10.1130/0091-7613(1999)027<0375:AMMPSL>2.3.CO;2.{{cite journal}}: CS1 maint: year (link)
  19. ^ Olson, S.L.; Hearty, P.J. (February 2009). "A sustained +21 m sea-level highstand during MIS 11 (400 ka): direct fossil and sedimentary evidence from Bermuda". Quaternary Science Reviews. 28 (3–4): 271–285. doi:10.1016/j.quascirev.2008.11.001.
  20. ^ van Hengstum, P.J.; Scott, D.B.; Javaux, E.J. (September 2009). "Foraminifera in elevated Bermudian caves provide further evidence for +21 m eustatic sea level during Marine Isotope Stage 11". Quaternary Science Reviews. 28: 1850–69. doi:10.1016/j.quascirev.2009.05.017.{{cite journal}}: CS1 maint: year (link)
  21. ^ Alberto V. Reyes; Anders E. Carlson; Brian L. Beard; Robert G. Hatfield; Joseph S. Stoner; Kelsey Winsor; Bethany Welke; David J. Ullman (June 25, 2014). "South Greenland ice-sheet collapse during Marine Isotope Stage 11". Nature. 510: 525–528. doi:10.1038/nature13456. PMID 24965655.
  22. ^ Pillans, Brad; Chappell, John; Naish, Tim R. (1998-12-01). "A review of the Milankovitch climatic beat: template for Plio–Pleistocene sea-level changes and sequence stratigraphy". Sedimentary Geology. 122 (1): 5–21. doi:10.1016/S0037-0738(98)00095-5.
  23. ^ Bowen, D. Q. (2010-01-19). "Sea level ~400 000 years ago (MIS 11): analogue for present and future sea-level?". Clim. Past. 6 (1): 19–29. doi:10.5194/cp-6-19-2010. ISSN 1814-9332.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  24. ^ Rohling, E. J.; Braun, K.; Grant, K.; Kucera, M.; Roberts, A. P.; Siddall, M.; Trommer, G. (2010-03-01). "Comparison between Holocene and Marine Isotope Stage-11 sea-level histories". Earth and Planetary Science Letters. 291 (1): 97–105. doi:10.1016/j.epsl.2009.12.054.
  25. ^ Muller, R.A.; MacDonald, G.J. (1997). "Glacial Cycles and Astronomical Forcing". Science. 277: 215–218. doi:10.1126/science.277.5323.215.
  26. ^ Wang, Xianfeng; Auler, Augusto S.; Edwards, R. Lawrence; Cheng, Hai; Cristalli, Patricia S.; Smart, Peter L.; Richards, David A.; Shen, Chuan-Chou (2004-12-09). "Wet periods in northeastern Brazil over the past 210 kyr linked to distant climate anomalies". Nature. 432 (7018): 740–743. doi:10.1038/nature03067. ISSN 0028-0836.
  27. ^ Jansen, J.H.F.; Kuijpers, A.; Troelstra, S.R. (1986-05-02). "A mid-Brunhes climatic event: long-term changes in atmosphere and ocean circulation". Science. 232.
  28. ^ Berger, Wolfgang H.; Jansen, Eystein (1994). Johannessen, O. M.; Muench, R. D.; Overland, J. E. (eds.). The Polar Oceans and Their Role in Shaping the Global Environment. American Geophysical Union. pp. 295–311. doi:10.1029/gm085p0295/summary. ISBN 9781118663882.
  29. ^ Ruddiman, William F. (2003-12-01). "The Anthropogenic Greenhouse Era Began Thousands of Years Ago". Climatic Change. 61 (3): 261–293. doi:10.1023/B:CLIM.0000004577.17928.fa. ISSN 0165-0009.
  30. ^ Broecker, Wallace S.; Stocker, Thomas F. (2006-01-17). "The Holocene CO2 rise: Anthropogenic or natural?". Eos, Transactions American Geophysical Union. 87 (3): 27–27. doi:10.1029/2006EO030002. ISSN 2324-9250.
  31. ^ Ruddiman, William F. (2007-12-01). "The early anthropogenic hypothesis: Challenges and responses". Reviews of Geophysics. 45 (4): RG4001. doi:10.1029/2006RG000207. ISSN 1944-9208.
  32. ^ Rohling, E. J.; Braun, K.; Grant, K.; Kucera, M.; Roberts, A. P.; Siddall, M.; Trommer, G. (2010-03-01). "Comparison between Holocene and Marine Isotope Stage-11 sea-level histories". Earth and Planetary Science Letters. 291 (1): 97–105. doi:10.1016/j.epsl.2009.12.054.


Saved MIS 11 Page

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5 million year history, representing the Lisiecki and Raymo (2005) LR04 Benthic Stack

Marine Isotope Stage 11 or MIS 11 is a Marine Isotope Stage in the geologic temperature record, covering the interglacial period between 424,000 and 374,000 years ago.[1] It corresponds to the geological Hoxnian Stage.

Interglacial periods which occurred during the Pleistocene are investigated to better understand present and future climate. Thus, the present interglacial, the Holocene, is compared with MIS 11 or Marine Isotope Stage 5.

Characteristics

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MIS 11 represents the longest and warmest interglacial interval of the last 500 kyr. In fact, it shows the highest-amplitude deglacial warming in the last 5 Myr and possibly lasted twice the other interglacial stages. MIS 11 is characterized by overall warm sea-surface temperatures in high latitudes, strong thermohaline circulation, unusual blooms of calcareous plankton in high latitudes, higher sea level than the present, coral reef expansion resulting in enlarged accumulation of neritic carbonates, and overall poor pelagic carbonate preservation and strong dissolution in certain areas. MIS 11 is considered the warmest interglacial period of the last 500,000 years.[2]

Concentration of CO2

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Carbon dioxide concentration during MIS 11 was possibly similar to that documented in the pre-industrial period, but not especially high when compared to other interglacial periods (for example, CO2 concentration was probably higher during MIS 9.[3] In addition, a peculiar feature of MIS 11 is that an early CO2 peak, usually associated to the deglaciation in response to increasing temperatures, is not detected.

Seemingly, the long-lasting interglacial conditions that are documented during MIS 11 depend on the peculiar interplay between CO2 concentration and insolation. In fact, during periods of both eccentricity and precession minima, even small variations in total insolation might lead the control of climate to greenhouse gasses, in particular CO2.

Carbonate productivity

[edit]

In shallow-water environments, the development of several major reef systems (such as the Great Barrier Reef) accompanied increased reef carbonate production. Calcium carbonate production peaked in subpolar and subtropical oceans, reflecting a shift in plankton ecology from diatoms to calcareous plankton due to changes in seawater temperatures, which were apparently warmer at low latitudes. The increased production of carbonate in either continental shelves and mid-latitude open-ocean environments may partly explain the high rates of carbonate sediments dissolution during MIS 11 throughout ocean basins, such as the Indian and Pacific. Indeed, increases in regional carbonate productivity can be only explained by increased carbonate dissolution in other (source) areas. Another explanation for the presence of barrier-reef tracts at low latitudes during MIS 11 is that tropical continental shelves were (at least partly) flooded in response to a major marine transgression (see below).

Sea level & marine transgression

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Marine core sections from the South Atlantic, about a million years old

Beach deposits in Alaska, Bermuda and the Bahamas, as well as uplifted reef terraces in Indonesia, suggest that global sea level reached as much as twenty metres above the present.[4][5][6] δ18
O records show isotopic depletions that are consistent with a sea-level highstand, but temperature effect cannot be confidently disentangled from glacioeustasy. Moreover, the collapse of at least one major ice sheet has to be inferred in order to produce similar high sea-levels, nevertheless, the stability of these ice sheets is one of the main questions in climate-change research: in fact, controversial geologic evidences suggest that present-day polar ice sheets might have been disrupted (or drastically shrunk) during previous Pleistocene interglacials.

The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that both the West Antarctica and the Greenland ice sheets were absent, or at least greatly reduced, during MIS 11. Sedimentary deposits from Greenland suggest a near-complete deglaciation of south Greenland, and a subsequent sea level rise of 4.5 to 6  metres of sea-level-equivalent volume during MIS 11, around 410,000 to 400,000  years ago.[7]

Astronomical features

[edit]

In contrast to most other interglacials of the late Quaternary, MIS 11 cannot be straightforwardly explained and modelled solely within the context of Milankovitch forcing mechanisms.[8] According to various studies, the MIS 11 interglacial period was longer than the other interglacial stages. The sustained interglacial warmth may have lasted as long as it did, because orbital eccentricity was low and the amplitude of the precessional cycle diminished, resulting in several fewer cold substages during this period and perhaps also induced abrupt climate change at MIS 12–11 transition, the most intense of the past 500 kyrs. It is notable that MIS 11 developed just after one of the most “heavy” Pleistocene δ18
O glacials (MIS 12). According to some authors, MIS 12 is likely to represent a “minimum” within the 400-kyr cyclicity (which is apparently “stretched” into ca. 500-kyr cycles in the Pleistocene), same as the MIS 24/MIS 22 complex (ca. 900 ka; Wang et al., 2004). In support of this inference is the observation that these dramatic glacial intervals are coincident with periods of major climate reorganisation, namely the “Mid-Brunhes Event” (Jansen et al., 1986) and the “Mid-Pleistocene Revolution” (Berger & Jansen, 1994), respectively. In view of its pattern of astronomically-driven insolation, MIS 11 may be the best analogue for the near future insolation situation. A 2-D Northern Hemisphere climate model used to simulate climate evolution over MIS 11, MIS 5 and into the future implied that the climatic features and length of MIS 11 may be comparable to the present-future interglacial in the absence of anthropogenic forcing. This consideration has led some authors to the conclusion that the current interglacial period (begun 10 kyr) would have continued for approximately 20–25 kyrs even in the absence of anthropogenic forcing.

See also

[edit]

References

[edit]
  1. ^ Lisiecki,Lorraine E.; Raymo, Maureen E. (2005). "A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records". doi:10.1029/2004PA001071.
  2. ^ Howard, W.R. (1997). "A warm future in the past". Nature. 388 (6641): 418–9. doi:10.1038/41201.
  3. ^ Raynaud, D.; Barnola, J.M.; Souchez, R.; Lorrain, R.; Petit, J.R.; Duval, P.; Lipenkov, V.Y. (July 2005). "Palaeoclimatology: the record for marine isotopic stage 11". Nature. 436 (7047): 39–40. doi:10.1038/43639b. PMID 16001055.
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Dtolson1 (talk) 21:27, 7 June 2017 (UTC)

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