CO2 in the Ice Core Record
Ice core basics
Several deep ice cores have been drilled from the vast ice sheets of Greenland and Antarctica, and in addition numerous cores have been obtained from many However, the different records often have their own timescales that are not consistent, so the records can not readily be compared in detail because one cannot. spikes observed in the depth profile of a South Pole ice core might correlate with . adjacent time markers is dated by assuming a constant MAR between them . Greenland Ice Sheet. Nature , – (). 3. Herron, M. M. Impurity Sources of F-, Cl-, NO3-, and SO4. 2- in Greenland and. Antarctic precipitation. Dent dating of Greenland and Antarctic ice cores by annual layer counting permits. et al., b), and consistent with the bipolar seesaw hy- pothesis ( Stocker. Tagged: One on one matchmaking chicago, Ex found me on a dating site, How to tell if your guy is just a hookup, Dating a guy a year younger in high school.
Communicated by Wallace S. The procedure is based on the assumption that the rapid changes in dust are associated with large-scale changes in atmospheric transport and implies that D—O oscillations in terms of their atmospheric imprint are more symmetric in form than can be inferred from Greenland temperature records.
After removal of the abrupt shifts the residual, dejumped dust record Consistent Hookup For Antarctic And Greenland Ice Cores found to match Antarctic climate variability with a temporal lag of several hundred years.
It is argued that such variability may reflect changes in the source region of Greenland dust thought to be the deserts of eastern Asia. Other records from this region and more globally also reveal Antarctic-style variability and suggest that this signal is globally pervasive.
This provides the potential basis for suggesting a more important role for gradual changes in triggering more abrupt transitions in the climate system. The discovery of repeated, abrupt, high-amplitude shifts in Northern Hemisphere climate during the last glacial period e. The millennial-scale Dansgaard—Oeschger D—O oscillations, first observed in temperature records from Greenland ice cores, are characterized by the repeated asymmetric alternation between cold stadial and warmer interstadial conditions Fig.
The close correspondence between temperature variations across the North Atlantic 3 — 5 and over Greenland leads to the argument for a direct physical connection between D—O variability and the mode of ocean circulation within the Atlantic basin 6. In contrast to that observed in Greenland, glacial age temperature variability recorded by Antarctic ice cores is characterized by a more gradual and symmetric behavior that is approximately out-of-phase with the high-latitude northern hemisphere 7 Fig.
This relationship provides the basis for the so-called bipolar seesaw hypothesis 89 whereby changes Hookup Miss 2018 Memes 2018 Ukraine ocean circulation associated with cooling warming across the North Atlantic and Greenland drive a corresponding warming cooling across the Southern Ocean and Antarctica.
However, the precise link between northern and southern ice-core temperature records has proven controversial 10 — More recently a direct relationship between the amplitude of warming in Antarctica and the duration of northern stadial events has been demonstrated 14providing clear evidence of a link between the northern and southern high latitudes on millennial time scales.
Upper numbers denote Heinrich events, and lower numbers denote canonical D—O events 2. Changes in Greenland dust during Heinrich stadials tend to resemble Antarctic temperature variability. In particular, atmospheric CO 2 variability during MIS 3 as well as on orbital time scales appears to be intimately related to regional changes around Antarctica and the Southern Ocean 24 — Here we demonstrate that a previously unrecognized Antarctic-style signal within the dust record from the Greenland Ice Sheet Project 2 GISP2 ice core in Greenland provides further evidence for a direct link between these bipolar climate archives and highlights the global influence of Antarctic-style climate variability during the last glacial period.
Ice cores continue reading both polar regions demonstrate that the Earth's this web page was significantly dustier during glacial times relative to the modern 27 Furthermore, high-resolution chemical records from Greenland ice Consistent Hookup For Antarctic And Greenland Ice Cores reveal a strong link between dust loading over Greenland and D—O temperature variability, with stadials being more dusty than interstadial periods 2829 Fig.
Dust records obtained from ice cores must be considered as a composite signal containing information about the supply of dust in the source region, its uplift to the high several km atmosphere and subsequent transport to the polar regions Previous studies have gone some way toward differentiating between the relative importance of these factors 28 — 30but explicit deconvolution between variations in source and transport is not straightforward.
Although the PCI is used to describe changes in large-scale atmospheric circulation, it implicitly includes variations in dust source extent and availability. However, the authors state that these vectors include both source area and transport effects. We develop this idea by starting with the basic premise that changes in the atmospheric circulation responsible for transporting dust to Greenland e.
This may be contrasted with those studies that start by assuming that the large-scale D—O jumps directly reflect source region variability e. We suggest that on millennial time scales the large D—O type jumps are superimposed on a Consistent Hookup For Antarctic And Greenland Ice Cores variability that reflects changes in the source region; the abrupt shifts are then telling us whether or not dust is focused toward Greenland.
Our argument stems from the visual observation that variations occurring before certain stadial—interstadial transitions in the GISP2 dust record appear to resemble Antarctic temperature variability Fig. Specifically, throughout stadial periods that contain Heinrich events, the level of dust tends to decrease continuously until the abrupt decrease associated with interstadial warming. Heinrich events tend to be associated with prolonged periods of warming in Antarctica, which themselves click the following article thought to be directly related to the extended duration of cold conditions over Greenland through the bipolar seesaw mechanism Indeed, the clearest evidence for decreasing stadial dust is seen during periods of significant warming in Antarctica.
Isolating the underlying source variability within the GISP2 dust record, as described above, requires the identification and removal of the rapid jumps associated with D—O transitions. To this end, we developed a numerical algorithm to pick D—O transitions based on the rapidity of changes in dust loading through time.
Picking D—O transitions using the Greenland dust record has the advantage over use of the temperature record thanks to the generally more obvious large and rapid transitions from interstadial to stadial as well as from stadial to interstadial state.
By our method all canonical D—O events 2 are identified in addition to a few others that tend to represent incomplete transitions between states [see supporting information SI Text and SI Fig. The defocusing function is similar to a trapezoidal wave form, alternating between two states; interstadial and stadial. The procedure therefore implies that stadial states were anomalously dusty the specific defocusing factor used for stadial periods is set to achieve maximum contiguity of the resulting dejumped record.
Only two focusing states are defined to maintain simplicity, although this may be too simplistic for the last glacial maximum LGM interval when the magnitude and direction of abrupt shifts appears less uniformed than for other intervals see SI Text. For this reason, the LGM is omitted from further discussion.
The procedure also implies that the atmospheric expression of D—O oscillations in Greenland ice cores is quite symmetric i. Dejumping the GISP2 dust record.
The Hidden World Beneath the Antarctic Ice Sheet
A From top to bottom are: AR is the Antarctic reversal. The DD record shows similar maximum correlative power to the unprocessed record but is shifted in time with maximum correlation attained when southern temperature leads DD by up to 1, yr.
C Same as B but without high-pass filtering.
In addition to the general increase in dustiness during the glacial period, millennial-scale decreases in DD tend to correspond to Antarctic warming events, whereas the deglacial Antarctic cold reversal is apparently aligned with a transient maximum in the DD record.
This observation begs the question: Does climatic variability in the source region of Greenland dust contain an Antarctic-type signature and hence suggest a more global nature of this signal? Also apparent in Fig. This is a direct effect of removing the abrupt D—O transitions, as illustrated by the presence of the same lag between the defocusing function and Antarctic temperature.
Therefore, the DD record is not a damped version of the raw dust record; rather, it is phase Consistent Hookup For Antarctic And Greenland Ice Cores and shows strongest negative correlation with Antarctic temperature with a lag of several hundred years behind the southern signal. This lag is also seen for the same records without orbital filtering Fig.
Although dejumping the dust record alters the phasing between northern and southern records, it does not improve the correlative power between the records. To test the hypothesis that climatic variability in the source region more closely matches Antarctic variability than it does Greenland it is click at this page to evaluate other records from this region and beyond.
Dust arriving at Greenland today and during the last glacial period is believed to originate in the deserts of eastern Asia 33 This is thought to be independent of changes between periods of high and low dust flux, at least during MIS 2 If the DD record describes changes in source region climate we may expect to find similar variability in other climate sensitive proxies from the same region. A high resolution speleothem record from Hulu cave in China 17 provides one such example Fig.
This record is thought to reflect changes in the intensity of the East Asian Monsoon and has previously been compared with the temperature record from Greenland.
We suggest that on millennial time scales the large D—O type jumps are superimposed on a background variability that reflects changes in the source region; the abrupt shifts are then telling us whether or not dust is focused toward Greenland. Although archives of precipitation are generally more complex than temperature, thicknesses of annual layers in ice cores provide some good information on precipitation. The links I have provided are for very reliable sources which can confidently be cited. Of particular relevance here is an apparent time lag of CO 2 behind Antarctic temperature.
The East Asian Monsoon originates in the WEP, the warmest part of the modern ocean and an important component of the global climate system. A high-resolution record of changing surface-ocean hydrographic conditions from this region during MIS 3 18 has also been correlated with conditions over Greenland Fig.
However, recent results from the East Equatorial Pacific show no clear evidence for a North Atlantic climate imprint in this region, source least at the millennial scale, and further show that climate variability during MIS 3 displayed somewhat similar behavior to Antarctic temperature variability Comparison between regional climate records.
A From top to bottom: Visually, the Hulu Cave and WEP records seem to share more similarity with the Antarctic records than they do with the Greenland record although the pronounced maxima in the Hulu Cave record correspond to North Atlantic Heinrich events.
C Same as Bbut including orbital-scale variability. From a visual inspection of the WEP and Hulu Cave records it is not immediately apparent that they should be aligned with Greenland temperature in preference to Antarctic climate variability see SI Text for details of age models. When placed on a linear age model, the WEP record seems to resemble records from Antarctica more closely than it does that from Greenland. For the interval, 60—30 kyr ago most relevant for D—O variabilityConsistent Hookup For Antarctic And Greenland Ice Cores WEP record correlates significantly better with records from Antarctica.
However, we do not advocate tuning the WEP record to either Greenland or Antarctica because this immediately implies some sort of mechanistic relationship that cannot be inferred from a similarity in appearance between the records. Nevertheless, our analysis Consistent Hookup For Antarctic And Greenland Ice Cores that the WEP record does contain an Antarctic-style climate signal. The case is less clear for the Hulu Cave record.
These effects include reduced precipitation over large parts of the northern hemisphere and increased rainfall in South America and Africa caused by a southward shift in the Intertropical Convergence Zone However, although the near-instantaneous effects of Heinrich AMOC collapses may be global, this does not necessarily imply that all D—O events should be expected to have the same influence.
Further evidence from Brazilian speleothems also suggests that southward migration of the ITCZ during MIS 3 was particularly pronounced only during Heinrich events, highlighting the anomalous conditions during these periods.
This schematic cross section of an ice sheet shows an ideal drilling site at the centre of the polar plateau near the ice divide, with ice flowing away from the ice divide in all direction. So atmospheric air is clearly being gradually mixt in to the sample in question for at least some hundreds even thousands of years. Leave a Reply Cancel reply Your email address will not be published. What is the sampling rate for the graphs shown above?
We argue that records such as that from Hulu Cave may well be expected to show a composite signal comprising the effects of near-instantaneous shifts in atmospheric circulation superimposed on a background variability that we contend reflects Antarctic-style climate fluctuations. This argument is based on the observation of the Antarctic signal in influential regions such as the tropical Pacific as well as its appearance in the DD record.
A question may then be raised concerning the DD record; should this not also reflect Heinrich events? In fact, the record does show maxima perhaps corresponding to the dry conditions associated with a weakened monsoon during Heinrich stadials.
This directly reflects the fact that the highest values in the raw dust record occur during these intervals Fig.
Asynchrony of Antarctic and Greenland climate change during the last glacial period | Nature
If records such as that from Hulu Cave and the surrounding region do contain signals of multiple origin notably D—O type variability superimposed upon an Click here modulation it is possible that the deconvolution method applied here may obscure D—O type variability associated with the source region as well as that associated with transport to Greenland.
Future work is required to better constrain the individual components of climate signals from this region and more generally. The observation of Antarctic-style climate variability in proxy records from remote settings such as the tropical Pacific and its appearance in the record of dust accumulation in Greenland suggest that this climate signal is more pervasive than perhaps previously assumed.
An immediate question is then what enables the global transmission of such a signal? For example, the close correspondence between Antarctic temperature and atmospheric CO 2 is well established for various time scales over the last kyr e.
This correspondence highlights the important role of the Southern Ocean for atmospheric CO 2 variability. Of particular relevance here is an apparent time lag of CO 2 behind Antarctic temperature. Several studies have attempted to quantify the precise phase relationship between these key variables. This is similar to the observed lag of our DD record behind Antarctic temperature as highlighted by the close Consistent Hookup For Antarctic And Greenland Ice Cores correspondence between CO 2 and the dejumped record when plotted on a common time scale Fig.
Antarctic climate signature in the Greenland ice core record
The fact that changes in atmospheric CO 2 lag behind Antarctic temperature variations does Consistent Hookup For Antarctic And Greenland Ice Cores diminish the potential role of CO 2 as a driver of climate change. All records are on the GISP2 time scale. The two records of CO 2 have been detrended by subtraction of a linear decrease of 0. Shaded gray areas loosely define warming periods in Antarctica. On the other hand it may be argued that CO 2 variations of 10—20 ppmv, as observed during MIS 3, might not have been sufficient to drive climatic changes see more as those implied by the DD record.
The oceans represent a potential alternative medium for transmission of the Antarctic signal quite beyond the fact that they may also represent the origin of this signal because changes in CO 2 themselves are likely to be driven by oceanic processes.
We have mentioned the observation of an Antarctic-style signal from several marine settings including the influential tropical surface Pacific. However, as yet there is no way to tune these records to investigate the precise temporal relationship between them and the high southern latitudes.
This represents an important step that should be tackled in the near future. One marine record that can be tuned to ice-core records with sufficient precision to address this issue is from core MD, taken at 3, m on the Iberian margin 5. The D—O oscillations provide the most dramatic example of abrupt climate variability during the last glacial cycle.