Kumiko Goto-Azuma

High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Years

The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition, reflecting the wetting of Asian deserts. A northern shift of the Intertropical Convergence Zone could be the trigger of these abrupt shifts of Northern Hemisphere atmospheric circulation, resulting in changes of 2 to 4 kelvin in Greenland moisture source temperature from one year to the next.

Ice core evidence for a very tight link between North Atlantic and east Asian glacial climate

[1] Corresponding millennial-scale climate changes have been reported from the North Atlantic region and from east Asia for the last glacial period on independent timescales only. To assess their degree of synchrony we suggest interpreting Greenland ice core dust parameters as proxies for the east Asian monsoon systems. This allows comparing North Atlantic and east Asian climate on the same timescale in high resolution ice core data without relative dating uncertainties. We find that during Dansgaard-Oeschger events North Atlantic region temperature and east Asian storminess were tightly coupled and changed synchronously within 5–10 years with no systematic lead or lag, thus providing instantaneous climatic feedback. The tight link between North Atlantic and east Asian glacial climate could have amplified changes in the northern polar cell to larger scales. We further find evidence for an early onset of a Younger Dryas-like event in continental Asia, which gives

The Mt Logan Holocene—late Wisconsinan isotope record: tropical Pacific—Yukon connections

The ice core recovered from Prospector Russell Col on Mt Logan (5.4 km a.s.l.), in the Yukon spans over 20 000 years. This unique record offers a Pacific view of the stable isotope and chemical record from the Lateglacial to the present. The timescale is based on seasonal counted years, the largest known volcanic acid signatures and the major shift in stable isotopes and chemistry at the end of the Younger Dryas. There are large and sustained changes in the stable isotopic record that are anti-correlated with marine and continental chemistry series. The oxygen-18 in this area is not a proxy for palaeotemperature but rather for source region. The last major isotope shift in AD 1840 in δ(18O) and chemistry is compared with the Quinns ENSO record. During periods of more frequent La Niña (stronger tropical easterlies) there is more zonal flow of water vapour transport to the Pacific Northwest, δ(18O) values are larger and the deuterium excess d smaller. These periods coincide with periods of lower accumulation/precipitation in southern Yukon. The Holocene δ(18O) record indicates many large shifts between the meridional (strong El Niño) and zonal (La Niña). Comparison of the Logan isotopic record and the moisture/temperature-sensitive time series of peat bog inception dates for the Northwest shows a strong correlation (0.36) that points to high accumulation rates coincident with low δ(18O) and enhanced meridional flow. Major changes in the core at 4200 BP and 7000—8000 BP point to enhanced meridional flow, which coincide with big changes in the Pacific palaeorecords of the balance between El Niño and La Niña. 4200 BP seems to have inaugurated the `modern ENSO world.

Seasonal variations of snow chemistry at NEEM, Greenland

Abstarct We conducted a pit study in July 2009 at the NEEM (North Greenland Eemian Ice Drilling) deep ice-coring site in northwest Greenland. To examine the seasonal variations of snow chemistry and characteristics of the drill site, we collected snow/firn samples from the wall of a 2 m deep pit at intervals of 0.03 m and analyzed them for electric conductivity, pH, Cl–, NO3 –, SO4 2–, CH3SO3 – (MSA), Na+, K+, Mg2+, Ca2+ and stable isotopes of water (δ18O and δD). Pronounced seasonal variations in the stable isotopes of water were observed, which indicated that the snow had accumulated regularly during the past 4 years. Concentrations of Na+, Cl– and Mg2+, which largely originate from sea salt, peaked in winter to early spring, while Ca2+, which mainly originates from mineral dust, peaked in late winter to spring, slightly later than Na+, Cl– and Mg2+. Concentrations of NO3 – showed double peaks, one in summer and the other in winter to spring, whereas those of SO4 2– peaked in winter to spring. The winter-to-spring concentrations of NO3 – and SO4 2– seem to have been strongly influenced by anthropogenic inputs. Concentrations of MSA showed double peaks, one in spring and the other in late summer to autumn. Our study confirms that the NEEM deep ice core can be absolutely dated to a certain depth by counting annual layers, using the seasonal variations of stable isotopes of water and those of ions. We calculated the annual surface mass balance for the years 2006–08. The mean annual balance was 176 mm w.e., and the balances for winter-to-summer and summer-to-winter halves of the year were 98 and 78 mm, respectively. Snow deposition during the winter-to-summer half of the year was greater than that during the summer-to-winter half by 10–20mm for all three years covered by this study.

State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling

Global cooling in intermediate glacial climate with northern ice sheets preconditions climatic instability with bipolar seesaw. Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.

Greenland 2012 melt event effects on CryoSat‐2 radar altimetry

CryoSat-2 data are used to study elevation changes over an area in the interior part of the Greenland Ice Sheet during the extreme melt event in July 2012. The penetration of the radar signal into dry snow depends heavily on the snow stratigraphy, and the rapid formation of refrozen ice layers can bias the surface elevations obtained from radar altimetry. We investigate the change in CryoSat-2 waveforms and elevation estimates over the melt event and interpret the findings by comparing in situ surface and snow pit observations from the North Greenland Eemian Ice Drilling Project camp. The investigation shows a major transition of scattering properties around the area, and an apparent elevation increase of 56 ± 26u2009cm is observed in reprocessed CryoSat-2 data. We suggest that this jump in elevation can be explained by the formation of a refrozen melt layer that raised the reflective surface, introducing a positive elevation bias.

Seasonal and spatial variations of snow chemistry on Mount Logan, Yukon, Canada

Abstract Three ice cores were recovered on or near Mount Logan, Yukon, Canada, at 3017, 4135 and 5340 ma.s.l. in 2002. Prior to ice-core drilling, we collected snow-pit and shallow core samples from Mount Logan in 2001 to study seasonal and spatial variations of snow chemistry. We dug snow pits at six sites between 2420 and 5340 m a.s.l. before the beginning of the melt season, with the exception of a pit at 3180 m a.s.l., where the melt season had just started but had affected only the near-surface stratigraphy. Three of the pits were extended deeper with a shallow core. The snow-pit and core samples were analyzed for ion chemistry and δ18O. A series of depth profiles of ions and δ18O shows spatial variations, though characteristic peaks can usually be traced across all the profiles. Concentrations and deposition fluxes of Na+ and Cl−, which are mainly of sea-salt origin, decrease with altitude. On the other hand, deposition fluxes of NO3 −, SO4 2–, Ca2+ and NH4 + show a weak positive relationship with elevation below the summit plateau. Stable isotopes (δ18O) decrease with altitude, with a distinctive jump between 3200 and 4500 m a.s.l., as was reported previously. Stable isotopes (δ18O), Cl−, CH3SO3 − (MSA), Na+ and Ca2+ show clear seasonal variations, which would enable us to date the cores by annual-layer counting.

Improved technique for measuring the size distribution of black carbon particles in liquid water

ABSTRACT We developed an improved technique for measuring the size distribution of black carbon (BC) particles suspended in liquid water to facilitate quantitative studies of the wet deposition of BC. The measurement system, which consists of a nebulizer and a single-particle soot photometer, incorporates two improvements into the system that we developed earlier. First, we extended the upper limit of the detectable BC size from 0.9 μm to about 4.0 μm by modifying the photo-detector for measuring the laser-induced incandescence signal. Second, we introduced a pneumatic nebulizer (Marin-5) with a high extraction efficiency (∼50.0%) that was independent of particle diameter up to 2.0 μm. For BC mass concentrations less than 70 μg L−1, we experimentally showed that the diameters of BC particles did not appreciably change during the Marin-5 extraction process, consistent with theoretical calculations. Finally, we demonstrated by laboratory experiments that the size distributions of ambient BC particles changed little during their growth into cloud droplets under supersaturation of water vapor. Using our improved system, we measured the size distributions of BC particles simultaneously in air and rainwater in Tokyo during summer 2014. We observed that the size distributions of BC particles in rainwater shifted to larger sizes compared with those observed in ambient air, indicating that larger BC particles in air were removed more efficiently by precipitation. Copyright

Modern solar maximum forced late twentieth century Greenland cooling

The abrupt Northern Hemispheric warming at the end of the twentieth century has been attributed to an enhanced greenhouse effect. Yet Greenland and surrounding subpolar North Atlantic remained anomalously cold in 1970s to early 1990s. Here we reconstructed robust Greenland temperature records (North Greenland Ice Core Project and Greenland Ice Sheet Project 2) over the past 2100u2009years using argon and nitrogen isotopes in air trapped within ice cores and show that this cold anomaly was part of a recursive pattern of antiphase Greenland temperature responses to solar variability with a possible multidecadal lag. We hypothesize that high solar activity during the modern solar maximum (approximately 1950s–1980s) resulted in a cooling over Greenland and surrounding subpolar North Atlantic through the slowdown of Atlantic Meridional Overturning Circulation with atmospheric feedback processes.

Asynchrony between Antarctic temperature and CO 2 associated with obliquity over the past 720,000 years

The δD temperature proxy in Antarctic ice cores varies in parallel with CO2 through glacial cycles. However, these variables display a puzzling asynchrony. Well-dated records of Southern Ocean temperature will provide crucial information because the Southern Ocean is likely key in regulating CO2 variations. Here, we perform multiple isotopic analyses on an Antarctic ice core and estimate temperature variations at this site and in the oceanic moisture source over the past 720,000 years, which extend the longest records by 300,000 years. Antarctic temperature is affected by large variations in local insolation that are induced by obliquity. At the obliquity periodicity, the Antarctic and ocean temperatures lag annual mean insolation. Further, the magnitude of the phase lag is minimal during low eccentricity periods, suggesting that secular changes in the global carbon cycle and the ocean circulation modulate the phase relationship among temperatures, CO2 and insolation in the obliquity frequency band.The Antarctic temperature record displays a puzzling asynchrony with changes in CO2 through glacial cycles. Here, the authors show that a 720,000-year Antarctic temperature record is affected by variations in obliquity-induced local insolation that are associated with phase modulation of eccentricity cycle.