Dansgaard–Oeschger-like events of the penultimate climate cycle: the loess point of view

The global character of the millennial-scale climate variability associated with the Dansgaard–Oeschger (DO) events in Greenland has been well-established for the last glacial cycle. Mainly due to the sparsity of reliable data, however, the spatial coherence of corresponding variability during the penultimate cycle is less clear. New investigations of European loess records from Marine Isotope Stage (MIS) 6 reveal the occurrence of alternating loess intervals and paleosols (incipient soil horizons), similar to those from the last climatic cycle. These paleosols are correlated, based on their stratigraphical position and numbers as well as available optically stimulated luminescence (OSL) dates, with interstadials described in various Northern Hemisphere records and in GLt_syn, the synthetic 800 kyr record of Greenland ice core δ18O. Therefore, referring to the interstadials described in the record of the last climate cycle in European loess sequences, the four MIS 6 interstadials can confidently be interpreted as DO-like events of the penultimate climate cycle. Six more interstadials are identified from proxy measurements performed on the same interval, leading to a total of 10 interstadials with a DO-like event status. The statistical similarity between the millennial-scale loess–paleosol oscillations during the last and penultimate climate cycle provides direct empirical evidence that the cycles of the penultimate cycle are indeed of the same nature as the DO cycles originally discovered for the last glacial cycle. Our results thus imply that their underlying cause and global imprint were characteristic of at least the last two climate cycles.

Parameterization of energy cycles between the hemispheres

Seasonal variations in the temperatures of the hemispheres induce seasonal energy cycles between the hemispheres that drive tropical cyclones. Because the northern hemisphere has warmed more than the southern hemisphere, climate energy cycles develop between the hemispheres as well. The seasonal and climate energy cycles appear to interact among themselves, and tropical cyclone counts are affected by these interactions. Furthermore, the total number of tropical cyclones appears to have an increasing trend. The annual energy of tropical cyclones is nearly 1.46 × 1022 J yr−1, and climate cycle energy is between 4.0 and 6.6 × 1021 J per cycle. The magnitude of the climate energy cycles is thus large enough to alter the energy and frequency of the tropical cyclones. Given that the climate is changing, the energy and frequency of tropical cyclones may be changing as well. The subject is broad and this work is limited to parameterization of the physics of energy oscillations between the hemispheres, demonstrating the existence of climate energy cycles, and revealing interactions between climate and seasonal energy cycles. Also, this parameterization may assist researchers in obtaining more and coordinated data relative to these cycles.

Orbital CO2 cycles and the Mid-Pleistocene Transition

<p>Over the past 1.5 million years, Earth’s climate has shifted from a predominantly 41 thousand year (kyr) dominated climate cycle to one dominated by longer and larger glacial-interglacial cycles, known as the Mid-Pleistocene Transition (MPT). The MPT occurs over a period of several hundreds of thousands of years, with little change to Earth’s external orbital forcing, thus implicating internal climate feedbacks. Here we interrogate the current capacity, and future potential, of boron isotope records to provide high quality carbon cycle information for the Pleistocene. We also present a compilation of boron isotope-derived pH-CO<sub>2</sub> records from low-latitude ocean drill cores which closely follow the evolution of atmospheric CO<sub>2 </sub>over the ice core interval but extend it to 1.5 million years ago with a resolution of up to ~1 sample per 3 kyr. This new, near continuous δ<sup>11</sup>B-derived CO<sub>2</sub> record is compared against other independent CO<sub>2</sub> data from blue-ice cores and records of ocean and climate change., This confirms there is a decline in mean CO<sub>2</sub> across the MPT which manifests as a lengthening and deepening of glacial CO<sub>2</sub>, and highlights the distinct difference in the nature of CO<sub>2</sub> cycles in the 41-kyr world.</p><p> </p>

DO-like events of the penultimate climate cycle: the loess point of view

The global character of the millennial-scale climate variability associated with the Dansgaard-Oeschger (DO) events in Greenland has been well-established for the last glacial cycle. Mainly due to the sparsity of reliable data, however, the spatial coherence of corresponding variability during the penultimate cycle is less clear. New investigations of European loess records from MIS 6 reveal the occurrence of alternating loess intervals and paleosols (incipient soil horizons), similar to those from the last climatic cycle. These paleosols are correlated based on their stratigraphical position and numbers, and available optically stimulated luminescence (OSL) dates with interstadials described in various Northern Hemisphere records as well as in GLt_syn, the synthetic 800-kyr record of Greenland ice core δ18O. Therefore, referring to the interstadials described in the record of the last climate cycle in European loess sequences, the MIS 6 interstadials can confidently be interpreted as DO-like events of the penultimate climate cycle. The statistical similarity between the millennial-scale loess-paleosol oscillations during the last and penultimate climate cycle provides direct empirical evidence that the cycles of the penultimate cycle are indeed of the same nature as the DO cycles originally discovered for the last glacial cycle. Our results thus imply that their underlying cause and global imprint was characteristic of at least the last two climate cycles.