More evidence the Medieval Warm Period was global

UPDATE: 3/30/12 Since a number of commenters that are getting bent out of shape over the issue can’t apparently be bothered to read the paper, and since the authors at Syracuse themselves are under pressure because the alarmosphere has gone ballistic over the possibility that Mike Mann’s “there is no MWP much less global” gospel might be challenged, I offer readers this passage from the actual paper:

The resolution of our record is insufficient to constrain

the ages of these climatic oscillations in the Southern

hemisphere relative to their expression in the Northern hemisphere, but our ikaite record builds the case that the oscillations of the MWP and LIA are global in their extent and their impact reaches as far South as the Antarctic Peninsula, while prior studies in the AP region

have had mixed results.

I realize that because the authors chose a really poor place to publish it, in Elsevier, which is being boycotted worldwide for their draconian policies on scientific publishing, that many people haven’t read the actual paper, but instead rely on others to interpret it for them, sparing them the effort of having to think or investigate for themselves. Of course the same sorts of people that claim my headline is wrong won’t believe the passage I’ve cited above, therefore I’m reproducing page 114 of the journal Earth and Planetary Science Letters 325–326 (2012) with the relevant passage highlighted:

Some media (The Daily Mail for example) have oversold the conclusions of the paper, and thus this is why the authors have issued a statement. Based on their words above in their own paper,  I stand by my headline.  Note that the authors at Syracuse have NOT asked me to change my headline nor any part of my post on the issue. – Anthony

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Oxygen 16/18 isotope ratios show the Medieval Warm Period was global – all the way to Antarctica

Despite this poorly written press release with the “topsy-turvy” first paragraph written by some PR person at Syracuse University who doesn’t even mention the name of the paper, there’s some interesting science in the paper once you figure out what the name of the paper is. Unfortunately, this is published by Elsevier, and like a growing number of people in the scientific community (8500+ now), I refuse to purchase anything from Elsevier (especially when they want $40 to read a paper already funded by taxpayers) since they pulled that stunt trying to lobby our legislature. Hopefully the authors themselves will liberate this important paper and put it on one of their own websites.  (Update: I’ve been in touch with Judy L. Holmes of Syracuse who has been very gracious. It seems Eurekalert botched the press release, excluding important info and that is now being corrected) – Anthony

Scientists use rare mineral to correlate past climate events in Europe, Antarctica

New study published in April issue of Earth and Planetary Science Letters

The first day of spring brought record high temperatures across the northern part of the United States, while much of the Southwest was digging out from a record-breaking spring snowstorm. The weather, it seems, has gone topsy-turvy. Are the phenomena related? Are climate changes in one part of the world felt half a world away?

To understand the present, scientists look for ways to unlock information about past climate hidden in the fossil record. A team of scientists led by Syracuse University geochemist Zunli Lu has found a new key in the form of ikaite, a rare mineral that forms in cold waters. Composed of calcium carbonate and water, ikaite crystals can be found off the coasts of Antarctica and Greenland.

“Ikaite is an icy version of limestone,” say Lu, assistant professor of earth sciences in SU’s College of Arts and Sciences. “The crystals are only stable under cold conditions and actually melt at room temperature.”

It turns out the water that holds the crystal structure together (called the hydration water) traps information about temperatures present when the crystals formed. This finding by Lu’s research team establishes, for the first time, ikaite as a reliable proxy for studying past climate conditions. The research was recently published online in the journal Earth and Planetary Science Letters and will appear in print on April 1. Lu conducted most of the experimental work for the study while a post-doctoral researcher at Oxford University. Data interpretation was done after he arrived at SU.

The scientists studied ikaite crystals from sediment cores drilled off the coast of Antarctica. The sediment layers were deposited over 2,000 years. The scientists were particularly interested in crystals found in layers deposited during the “Little Ice Age,” approximately 300 to 500 years ago, and during the “Medieval Warm Period,” approximately 500 to 1,000 years ago. Both climate events have been documented in Northern Europe, but studies have been inconclusive as to whether the conditions in Northern Europe extended to Antarctica.

Ikaite crystals incorporate ocean bottom water into their structure as they form. During cooling periods, when ice sheets are expanding, ocean bottom water accumulates heavy oxygen isotopes (oxygen 18). When glaciers melt, fresh water, enriched in light oxygen isotopes (oxygen 16), mixes with the bottom water. The scientists analyzed the ratio of the oxygen isotopes in the hydration water and in the calcium carbonate. They compared the results with climate conditions established in Northern Europe across a 2,000-year time frame. They found a direct correlation between the rise and fall of oxygen 18 in the crystals and the documented warming and cooling periods.

“We showed that the Northern European climate events influenced climate conditions in Antarctica,” Lu says. “More importantly, we are extremely happy to figure out how to get a climate signal out of this peculiar mineral. A new proxy is always welcome when studying past climate changes.”

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An ikaite record of late Holocene climate at the Antarctic Peninsula

http://www.sciencedirect.com/science/article/pii/S0012821X12000659

Zunli Lu, Rosalind E.M. Rickaby, Hilary Kennedy, Paul Kennedy, Richard D. Pancost, Samuel Shaw, Alistair Lennie, Julia Wellner, John B. Anderson

Abstract

Calcium carbonate can crystallize in a hydrated form as ikaite at low temperatures. The hydration water in ikaite grown in laboratory experiments records the δ¹⁸O of ambient water, a feature potentially useful for reconstructing δ¹⁸O of local seawater. We report the first downcore δ¹⁸O record of natural ikaite hydration waters and crystals collected from the Antarctic Peninsula (AP), a region sensitive to climate fluctuations. We are able to establish the zone of ikaite formation within shallow sediments, based on porewater chemical and isotopic data. Having constrained the depth of ikaite formation and δ¹⁸O of ikaite crystals and hydration waters, we are able to infer local changes in fjord δ¹⁸O versus time during the late Holocene. This ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula.

UPDATE: A colleague has forwarded a copy of the paper, allowing me to cite some additional information that I have presented below:

From the discussion section:

…

The MWP has not yet been unambiguously established around the

AP. Three δ18Ohydra values fall in this period and all of them are significantly

lighter than those values of older crystals by 2–3‰, a difference

too large to be explained by analytical uncertainties and

variability among crystals formed at the same time (0.33‰ at

JPC24), and are associated with lower δ18OCaCO3.We tentatively interpret

this shift in ikaite isotopic values as the result of meltwater invasion,

and warming in the Firth of Tay during the MWP. The ~5‰

decrease in δ18Ohydra at the beginning of the MWP must indicate

very strong freshening at the bottom of fjord, likely due to meltwater

cascading to depth. How such a distinct isotopic signal might be preserved

to such great depth in the fjord is beyond the scope of this

paper. However, meltwater beneath the ice-sheet is known to be

injected into fjords at different water depths including the base of

the fjord (Domack and Ishman, 1993). Although meltwater typically

mixes quickly with fjord water, it can be trapped at the base of the

inner fjord sometimes (e.g. when there is a sill preventing it from

moving forward) (Domack and Ishman, 1993). We hypothesize that

such subglacial meltwater may be the cause of strong meltwater signal

at the beginning of MWP. Other evidence supports the meltwater

signal inferred from δ18Ohydra. At the Firth of Tay, MS shifted to mostly

below average values between 1 and 0.6 ka (Fig. 6A). Low MS was

also found for the same period of time in Bransfield Strait sediments

and was considered to mark the MWP (Khim et al., 2002). Elemental

ratio records from Maxwell Bay, northern Bransfield Strait, allow

identification of both the MWP and the Little Ice Age (Monien et al.,

2011). Moss exposed by recent ice retreat on Anvers Island, West

AP, were radiocarbon dated to 0.7–0.97 ka, contrary to the much

older ages of reworked marine shells in the same sections, indicating

that the ice-sheet was reduced during that period to an extent of similar

magnitude to today (Hall et al., 2010). δ18OEPICA (Stenni et al.,

2006) shows warming at 0.6–0.8 ka, but with a brief cooling in between.

SST at Palmer Deep was even higher than modern during

this period (Shevenell et al., 2011). There is a notable lag between

the onset of MWP at the western AP and at the eastern AP according

to this SST record and our ikaite record although this observation

needs to be confirmed by additional records. On the eastern AP, no

significant change in foraminifera assemblage at Firth of Tay was observed

that could correspond with the Medieval Warm Period, Little

Ice Age, or the warming over the last century (Majewski and

Anderson, 2009). Also signals of the MWP or LIA, if any, were not

up to a magnitude that influenced glacial sedimentation

(Michalchuk et al., 2009).

…

Our most recent crystals suggest a warming relative to

the LIA in the last century, possibly as part of the regional recent

rapid warming, but this climatic signature is not yet as extreme in nature

as the MWP. The resolution of our record is insufficient to constrain

the ages of these climatic oscillations in the Southern

hemisphere relative to their expression in the Northern hemisphere,

but our ikaite record builds the case that the oscillations of the

MWP and LIA are global in their extent and their impact reaches as

far South as the Antarctic Peninsula, while prior studies in the AP region

have had mixed results.

Conclusions

We report the first comprehensive geochemical study on an

ikaite-containing core to demonstrate the potential of using hydration

water δ18Ohydra as a paleoenvironmental proxy. Porewater solute

concentrations indicate that these authigenic carbonate minerals

form in a narrow and shallow zone where Ca and DIC are both relatively

enriched. Coupling δ13C of ikaite crystals and δ13C of porewater

DIC, allows estimation of formation depth for individual crystal. The

ikaite formation depths are then used to calculate the time of crystallization

relative to the ambient sediments. δ18Ohydra and δ18OCaCO3

throughout JPC2 at Firth of Tay are reported. The youngest crystal

precipitated in modern porewater validates the fractionation factor

obtained in the previous study (Rickaby et al., 2006). The late Holocene

climate pattern inferred from δ18Ohydra and δ18OCaCO3 is comparable

to other records from the region and our ikaite record provides

new support that the MWP and LIA might have influenced the AP. In

the future, paired δ18Ohydra and δ18OCaCO3 may be used to calculate

δ18O of paleo-porewater indicating temperature changes. At this

stage, the geochemistry of ikaite serves as a qualitative, rather than

a quantitative, climatic proxy, because it remains challenging to account

for kinetic effects on uptake of δ18O into the carbonate during

crystallization and any post-crystallization exchange of δ18Ohydra

signal.