I thought to open a discussion on the science related to the Bølling-Allerød warming, a period with exceptional rate of changes, as recorded in ice core records from Greenland/Northern Greenland. Then there is science related to the AMOC, and Volcanism.
Bølling–Allerød Interstade (BA), is a widespread abrupt warming event in the Northern Hemisphere during the deglacial transition, essentially synchronous in Alaska and Greenland (Praetorius and Mix, 2014).
The sea-surface warming of ∼3 ◦C in the Gulf of Alaska (GOA) record occurs abruptly (in <90 yrs), consistent with ice-core records that register this transition as occurring within decades (Steffensen et al., 2008).
https://www.researchgate.net/publication/306418361_Interaction_between_climate_volcanism_and_isostatic_rebound_in_Southeast_Alaska_during_the_last_deglaciation The question is what causes the abrupt warming at the onset of the Bølling as seen in the Greenland ice cores. There is a clear antiphasing seen in the deglaciation interval between 20 and 10 ka. During the first half of this period, Antarctica steadily warmed, but little change occurred in Greenland. Then, at the time when Greenland’s climate underwent an abrupt warming, the warming in Antarctica stopped. A possible hypothesis can be that a sudden increase of the northward heat transport draws more heat from the south, and leads to a strong warming in the north. This “heat piracy” from the South Atlantic has been formulated by Crowley (1992). A logical consequence of this heat piracy is the Antarctic Cold Reversal (ACR) during the Northern Hemisphere warm Bølling/Allerød.
http://epic.awi.de/41137/1/polfor_2016_013.pdfThe bottom line seems to me, to identify involved mechanisms, but to be careful to draw conclusions as analog for today's climate, with different configurations, loading, and rates or warming. However, responsible mechanism are very likely to take part this time around as well, but might act differently, ie. AMOC, response times, regional differences.
Below a link to an excerpt by Jim White with a brief comment on the event, and a couple of related studies.
Abrupt Climate Change explained by Jim White, 12 Minutes excerpt (@AGU 2014)
https://www.youtube.com/watch?v=siWCXOypJh4&feature=youtu.be&t=3m15sJuly 16, 2009 BOULDER—By simulating 8,000 years of climate with unprecedented detail and accuracy, a team led by scientists from the University of Wisconsin–Madison and the National Center for Atmospheric Research (NCAR) has found a new explanation for the last major period of global warming, which occurred about 14,500 years ago.
In a period called the Bølling-Allerød warming, global sea level rose by 16 feet and temperatures in Greenland soared by up to 27 degrees Fahrenheit over several hundred years. The new study shows how increased carbon dioxide, strengthening ocean currents, and a release of ocean-stored heat could have combined to trigger the warming.
https://www2.ucar.edu/atmosnews/news/809/new-cause-past-global-warming-revealed-massive-modeling-project2016
On the Abruptness of Bølling–Allerød WarmingUsing a high-resolution TCC-resolved regional model, it is found that this decadal-scale accumulation of OCAPE ultimately overshoots its intrinsic threshold and is released abruptly (~1 month) into kinetic energy of TCC, with further intensification from cabbeling. TCC has convective plumes with approximately 0.2–1-km horizontal scales and large vertical displacements (~1 km), which make TCC difficult to be resolved or parameterized by current general circulation models. The simulation herein indicates that these local TCC events are spread quickly throughout the OCAPE-contained basin by internal wave perturbations. Their convective plumes have large vertical velocities (~8–15 cm s−1) and bring the WSW to the surface, causing an approximate 2°C sea surface warming for the whole basin (~700 km) within a month. This exposes a huge heat reservoir to the atmosphere, which helps to explain the abrupt Bølling–Allerød warming.
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0675.1Related talk from AGU 2014 Thermobaric instability / and modelling of warm salty water getting to the surface. The role of the ocean in the last deglaciation
2017
The Atlantic Meridional Overturning Circulation and Abrupt Climate ChangeAbrupt changes in climate have occurred in many locations around the globe over the last glacial cycle, with pronounced temperature swings on timescales of decades or less in the North Atlantic. The global pattern of these changes suggests that they reflect variability in the Atlantic meridional overturning circulation (AMOC). This review examines the evidence from ocean sediments for ocean circulation change over these abrupt events. The evidence for changes in the strength and structure of the AMOC associated with the Younger Dryas and many of the Heinrich events is strong. Although it has been difficult to directly document changes in the AMOC over the relatively short Dansgaard-Oeschger events, there is recent evidence supporting AMOC changes over most of these oscillations as well. The lack of direct evidence for circulation changes over the shortest events leaves open the possibility of other driving mechanisms for millennial-scale climate variability.
http://annualreviews.org/doi/abs/10.1146/annurev-marine-010816-0604152016
Abrupt Bølling warming and ice saddle collapse contributions to the Meltwater Pulse 1a rapid sea level rise Elucidating the source(s) of Meltwater Pulse 1a, the largest rapid sea level rise caused by ice melt (14–18 m in less than 340 years, 14,600 years ago), is important for understanding mechanisms of rapid ice melt and the links with abrupt climate change. Here we quantify how much and by what mechanisms the North American ice sheet could have contributed to Meltwater Pulse 1a, by driving an ice sheet model with two transient climate simulations of the last 21,000 years. Ice sheet perturbed physics ensembles were run to account for model uncertainties, constraining ice extent and volume with reconstructions of 21,000 years ago to present. We determine that the North American ice sheet produced 3–4 m global mean sea level rise in 340 years due to the abrupt Bølling warming, but this response is amplified to 5–6 m when it triggers the ice sheet saddle collapse.
http://onlinelibrary.wiley.com/doi/10.1002/2016GL070356/full2014 An ice core record of near-synchronous global climate changes at the Bølling transition
http://www.nature.com/ngeo/journal/v7/n6/abs/ngeo2147.html2014 Abrupt pre-Bølling–Allerød warming and circulation changes in the deep ocean
http://www.nature.com/nature/journal/v511/n7507/abs/nature13472.htmlhttps://en.wikipedia.org/wiki/B%C3%B8lling-Aller%C3%B8dVolcanism linked to BARelated
Modelling suggests with ice cap melt, an increase in volcanic activity http://climatestate.com/2014/10/16/methane-hydrate-destabilisation-is-clearly-a-real-worry-particularly-in-the-context-of-warming-ocean-waters-in-the-east-siberian-continental-shelf/2016
Interaction between climate, volcanism, and isostatic rebound in Southeast Alaska during the last deglaciationWe evaluate the timing and climate context of a deglacial volcanic sequence from Southeast Alaska.
We document an increase in volcanism in response to deglacial ice loss and isostatic rebound.
These data support the hypothesis that regional deglaciation can rapidly trigger volcanic activity.
An increase in regional climate variability is associated with the interval of intense volcanism.
This study illustrates a two-way coupling of climate and volcanism across time scales.
The sudden increase in volcanic activity from the MEVF coincides with the onset of Bølling–Allerød interstadial warmth, the disappearance of ice-rafted detritus, and rapid vertical land motion associated with modeled regional isostatic rebound in response to glacier retreat. These data support the hypothesis that regional deglaciation can rapidly trigger volcanic activity. Rapid sea surface temperature fluctuations and an increase in local salinity (i.e., δ18Osw) variability are associated with the interval of intense volcanic activity, consistent with a two-way interaction between climate and volcanism in which rapid volcanic response to ice unloading may in turn enhance short-term melting of the glaciers, plausibly via albedo effects on glacier ablation zones.
http://www.sciencedirect.com/science/article/pii/S0012821X16303892 https://www.researchgate.net/publication/306418361_Interaction_between_climate_volcanism_and_isostatic_rebound_in_Southeast_Alaska_during_the_last_deglaciationTwo plausible mechanisms could have linked the interval of isostatic adjustment with enhanced volcanism: 1) increased melt production generated through decompression in the shallow mantle (Maclennan et al., 2002), or 2) reduced storage time of crustal magmas through regional adjustment in crustal stress and enhanced dike formation (Rawson et al., 2016). The near-zero timelag between regional isostatic adjustment and an abrupt increase in volcanic eruptive frequency in Southeast Alaska suggests the latter scenario is more plausible, or at least the dominant mechanism.
Supporting this supposition is the rapid mobilization of differentiated magma through multiple vents. Decompression melting would not likely have produced differentiated magmas on the time-frames observed, while previous work by others has shown that the Mount Edgecumbe magma chamber likely contained cupolas above the main basaltic chamber that already contained the more siliceous material (e.g. Myers and Sinha, 1985; Riehle et al., 1992b).
The rapid response of the Southeast Alaska system contrasts with inferred lags of volcanism several thousand years behind sealevel rise in global compilations (Kutteroff et al., 2013; Watt et al., 2013). It is plausible to think that some volcanic systems may have longer lag times behind local unloading; for example, arc systems in thicker continental crust may have longer response times (Rawson et al., 2016) than relatively isolated volcanic systems with shallow magma chambers, such as in Southeast Alaska (Riehle et al., 1994). Nevertheless, our findings highlight the importance of well-constrained regional studies to understand the rates and sensitivity of interactions between surface processes and volcanic activity.
The δ18Osw reconstruction reveals low values, implying freshening of surface waters, between 14.6 and 14.0 ka. Although the rapid freshening of surface waters coincides with abrupt warming, the interval of freshening is not uniquely linked to the warmest temperatures, as there are intervals within the BA with equivalently high SSTs that do not show an apparent decrease in δ18Osw.
The interval with greatest apparent freshening and high variance in δ18Osw coincides with the interval of deposition of basaltic tephra, which is coeval with the rapid warming and disappearance of ice-rafted debris (IRD) at the onset of the Bølling Interstade (Fig. 5, Fig. S5). Although these initial tephra layers are thin (0.5 cm), the deposition of dark tephra in the ablation zone of glaciers could have reduced albedo of the snow and ice surfaces (Conway et al., 1996), thereby promoting rapid melting and accelerated local meltwater output along with deglaciation. This mechanism would likely have enhanced freshwater runoff into the Alaskan coastal currents during deglaciation, and this influx of low δ18O water would in turn have influenced the isotopic composition of near-surface waters.
Although firm attribution of specific causal relationships is difficult with only a few events, it is plausible that both hemispheric and regional forcings contribute to climate variability in the GOA region. While direct radiative-forcing effects from individual eruptions are unlikely to lead to long-term cooling due to the relatively short residence time of volcanic aerosols in the upper atmosphere (1–3 yrs), a prolonged increase in the frequency of eruptions could lead to either warming or cooling perturbations through ice-albedo, sea-ice, or CO2 feedbacks.
Modeling studies suggest that hemispheric cooling of decades to centuries can be initiated by the effects of multiple eruptions (McGregor et al., 2015; Pollack et al., 1993), or sea-ice feedbacks (Miller et al., 2012).
Sustained intervals of volcanism during the deglaciation may also have contributed to warming through increased CO2 emissions (Huybers and Langmuir, 2009), and ice-albedo feedbacks. Tephra deposited in the ablation zone of glaciers accelerates melting because the tephra (>5 μm) tends to remain at the ice surface as the glacier retreats (Conway et al., 1996).
Tephra that was once covered in the accumulation zone will at some point be uncovered in the ablation zone, where its growing concentration at the ice surface may provide a feedback for glacial melting in models (Peltier and Marshall, 1995).
In some instances thick ash (>10 mm) can act as a short-term insulating layer on glaciers (Dragosics et al., 2016), delaying melting in areas proximal to the vent, but the wider dispersal of finer ash particles will likely more than compensate this localize insulating effect through a greater surface area over which thin tephra layers will act to increase ablation rates.
Given the evidence for rapid retreat of marine terminating glaciers preceding/coinciding with the interval of frequent volcanic tephra deposition from the MEVF, it is plausible that tephra deposited on these regional glaciers would have an nearly immediate impact on melt rates in the already-expanding ablation zones. Thus, rapid responses of Alaskan volcanic systems to initial deglaciation may have accelerated ice losses in the region.
The large number of volcanoes in the Pacific “Ring of Fire”, coupled with the prevailing westerly winds, make deposition of tephra on the Laurentide and Cordilleran ice sheets (Fig. 1) a potential contributor to glacial wasting and ice-sheet instability
Greenhouse gases are considered one of the powerful feedback mechanisms in the ice age cycle. Might deglacial volcanism contribute to this effect? The rise of atmospheric CO2 during the first half of the deglaciation (18–15 ka) was likely sourced primarily from processes related to organic matter, as shown by δ13C (Schmitt et al., 2012; Bauska et al., 2016), plausibly through a decrease in the net strength of the ocean’s biological pump, which yields CO2 depleted in 13C relative to the atmosphere.
Later in the deglaciation (<15 ka), further trends of rising CO2 are not associated with long-term 13C depletion, and therefore could include contributions from either ocean warming or volcanic CO2, which both yield CO2 rise not depleted in 13C relative the background atmospheric values. Superimposed in these larger trends are abrupt (∼10 ppm) rises in atmospheric CO2 near 16–16.5 ka, 14.5–14.7 ka, and 11.5–12 ka (Marcott et al., 2014).
Carbon isotope data from ice core CO2 constrain the youngest and oldest of these abrupt rises to be sourced primarily from organic carbon reservoirs, most likely on land (Bauska et al., 2016), but could allow partial contributions from other sources including volcanic CO2.
The abrupt rise in atmospheric CO2 near 14.7–14.5 ka, however, has no discernable change in atmospheric δ13C (Bauska et al., 2016) implying that it cannot be sourced from oxidation of organic matter and therefore may be consistent with volcanic sources that responded relatively quickly to deglacial unloading.
This finding is consistent with the hypothesis that ice-unloading can trigger volcanism. We find no significant lag between the timing of major ice retreat and the onset of volcanism, suggesting that the volcanic response to deglaciation is rapid in this region. Between 14.6–13.1 ka, the MEVF exhibited an eruption recurrence interval of ∼1.5 events/century based on the macroscopic tephra-fall units identified in this study.
Early in the eruptive sequence, basaltic tephra is associated with surface water freshening (implied by anomalously low δ18Osw), suggesting that in this region, volcanism triggered by deglacial unloading may plausibly accelerate melting and water runoff through an albedo effect of dark tephra on snow and ice. With this insight from a well constrained regional study, re-examination of the integrated sulfate record from the Greenland ice core suggests that sustained early deglacial volcanism could accelerate rapid melting of some northern hemisphere glaciers through a reduction in surface albedo. Regional volcanism may thus play a significant role in century-to millennial scale climate change during the deglaciation.
BA and AMOC2016
Abrupt Climate Change Experiments: The Role of Freshwater, Ice Sheets and Deglacial Warming for the Atlantic Meridional Overturning Circulation http://epic.awi.de/41137/1/polfor_2016_013.pdf
