High-latitude Southern Hemisphere fire history during the mid- to late Holocene (6000–750 BP)

Abstract. We determined the specific biomass burning biomarker levoglucosan in an ice core from the TALos Dome Ice CorE drilling project (TALDICE) during the mid- to late Holocene (6000–750 BP). The levoglucosan record is characterized by a long-term increase with higher rates starting at ∼ 4000 BP and peaks between 2500 and 1500 BP. The anomalous increase in levoglucosan centered at ∼ 2000 BP is consistent with other Antarctic biomass burning records. Multiple atmospheric phenomena affect the coastal Antarctic Talos Dome drilling site, where the Southern Annular Mode (SAM) is the most prominent as the Southern Annular Mode Index (SAMA) correlates with stable isotopes in precipitation throughout the most recent 1000 years of the ice core. If this connection remains throughout the mid- to late Holocene, then our results demonstrate that changes in biomass burning, rather than changes in atmospheric transport, are the major influence on the TALDICE levoglucosan record. Comparisons with charcoal syntheses help evaluate fire sources, showing a greater contribution from southern South American fires than from Australian biomass burning. The levoglucosan peak centered at ∼ 2000 BP occurs during a cool period throughout the Southern Hemisphere, yet during a time of increased fire activity in both northern and southern Patagonia. This peak in biomass burning is influenced by increased vegetation in southern South America from a preceding humid period, in which the vegetation desiccated during the following cool, dry period. The Talos Dome ice core record from 6000 to ∼ 750 BP currently does not provide clear evidence that the fire record may be strongly affected by anthropogenic activities during the mid- to late Holocene, although we cannot exclude at least a partial influence.

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High latitude Southern Hemisphere fire history during the Mid-Late Holocene (750–6000 yr BP)

10.5194/cp-2017-158 ◽

2017 ◽

Author(s):

Dario Battistel ◽

Natalie M. Kehrwald ◽

Piero Zennaro ◽

Giuseppe Pellegrino ◽

Elena Barbaro ◽

...

Keyword(s):

Southern Hemisphere ◽

Biomass Burning ◽

High Latitude ◽

Late Holocene ◽

Fire History ◽

Climatic Factors ◽

Atmospheric Transport ◽

Ice Core ◽

Ice Cores ◽

Transport Pathway

Abstract. Abstract. High latitude Southern Hemisphere fire history was reconstructed by determining the specific biomarker levoglucosan in ice cores from the TALos Dome Ice CorE drilling project (TALDICE) during the Mid-Late Holocene (750–6000 yr BP). Potassium was also analyzed in order to provide a comparison with another fire proxy to create a more robust biomass burning record. The levoglucosan record is characterized by a long-term increase with higher rates starting at ~ 4000 yr BP and higher peaks between 1500 and 2500 yr BP. Comparisons with charcoal syntheses help evaluate fire sources, showing a possible higher contribution from Patagonian fires rather than Australian biomass burning. We interpret the anomalous increase in levoglucosan centred at ~ 2000 yr BP as a combination of the atmospheric transport pathway and the interplay between climatic factors.

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The impact of the Southern Annular Mode on future changes in Southern Hemisphere rainfall

Geophysical Research Letters ◽

10.1002/2016gl069453 ◽

2016 ◽

Vol 43 (13) ◽

pp. 7160-7167 ◽

Cited By ~ 42

Author(s):

Eun-Pa Lim ◽

Harry H. Hendon ◽

Julie M. Arblaster ◽

Francois Delage ◽

Hanh Nguyen ◽

...

Keyword(s):

Southern Hemisphere ◽

Southern Annular Mode ◽

Annular Mode ◽

The Impact

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Southern Hemisphere Annular Mode Variability and the Role of Optimal Nonmodal Growth

Journal of the Atmospheric Sciences ◽

10.1175/jas3444.1 ◽

2005 ◽

Vol 62 (6) ◽

pp. 1947-1961 ◽

Cited By ~ 9

Author(s):

Harun A. Rashid ◽

Ian Simmonds

Keyword(s):

Southern Hemisphere ◽

Zonal Wind ◽

Positive Feedback ◽

General Model ◽

Initial Perturbation ◽

Low Frequency ◽

Southern Annular Mode ◽

Feedback Mechanism ◽

Annular Mode ◽

Positive Feedback Mechanism

Abstract The southern annular mode is the leading mode of Southern Hemisphere circulation variability, the temporal evolution of which is characterized by large amplitudes and significant persistence. Previous investigators have suggested a positive feedback mechanism that explains some of this low-frequency variance. Here, a mechanism is proposed, involving transient nonmodal growths of the anomalies, that is at least as effective as the positive feedback mechanism in increasing the low-frequency variance of the southern annular mode. Using the vector autoregressive modeling technique, a number of linear inverse models of southern annular mode variability from National Centers for Environmental Prediction–Department of Energy (NCEP–DOE) Reanalysis 2 is derived. These models are then analyzed applying the ideas of the generalized stability theory. It is found that, as a consequence of the nonnormality of the system matrices, a significant increase in the low-frequency variance of the southern annular mode occurs through optimal nonmodal growth of the zonal wind anomalies. The nonnormality arises mainly from the relative dominance of the eddy forcing, while the nonmodal growth is caused by the interference of the nonorthogonal eigenvectors of the nonnormal system matrix. These results are demonstrated first in a simple model that retains only the two leading modes of the zonally averaged zonal wind and eddy-forcing variability, and then in a more general model that includes all the important modes. Using the more general model the authors have determined, among other things, the optimal initial perturbation and the time scale over which it experiences the maximum nonmodal growth to evolve into the pattern associated with the southern annular mode.

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Impacts of a Midlatitude Oceanic Frontal Zone for the Baroclinic Annular Mode in the Southern Hemisphere

Journal of Climate ◽

10.1175/jcli-d-20-0359.1 ◽

2021 ◽

pp. 1-63

Author(s):

MORIO NAKAYAMA ◽

HISASHI NAKAMURA ◽

FUMIAKI OGAWA

Keyword(s):

Southern Hemisphere ◽

General Circulation ◽

Frontal Zone ◽

Circulation Model ◽

Southern Annular Mode ◽

Internal Dynamics ◽

Near Surface ◽

Annular Mode ◽

Major Mode ◽

Sst Gradient

AbstractAs a major mode of annular variability in the Southern Hemisphere, the baroclinic annular mode (BAM) represents the pulsing of extratropical eddy activity. Focusing mainly on sub-weekly disturbances, this study assesses the impacts of a midlatitude oceanic frontal zone on the BAM and its dynamics through a set of “aqua-planet” atmospheric general circulation model experiments with zonally uniform sea-surface temperature (SST) profiles prescribed. Though idealized, one experiment with realistic frontal SST gradient reasonably well reproduces observed BAM-associated anomalies as a manifestation of a typical lifecycle of migratory baroclinic disturbances. Qualitatively, these BAM features are also simulated in the other experiment where the frontal SST gradient is removed. However, the BAM-associated variability weakens markedly and shifts equatorward, in association with the corresponding modifications in the climatological-mean stormtrack activity. The midlatitude oceanic frontal zone amplifies and anchors the BAM variability by restoring near-surface baroclinicity through anomalous sensible heat supply from the ocean and moisture supply to cyclones, although the BAM is essentially a manifestation of atmospheric internal dynamics. Those experiments and observations further indicate that the BAM modulates momentum flux associated with transient disturbances to induce a modest but robust meridional shift of the polar-front jet, suggesting that the BAM can help maintain the southern annular mode. They also indicate that the quasi-periodic behavior of the BAM is likely to reflect internal dynamics in which atmospheric disturbances on both sub-weekly and longer time scales are involved.

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Five thousand years of fire history in the high North Atlantic region: natural variability and ancient human forcing

Climate of the Past ◽

10.5194/cp-17-1533-2021 ◽

2021 ◽

Vol 17 (4) ◽

pp. 1533-1545

Author(s):

Delia Segato ◽

Maria Del Carmen Villoslada Hidalgo ◽

Ross Edwards ◽

Elena Barbaro ◽

Paul Vallelonga ◽

...

Keyword(s):

Black Carbon ◽

Biomass Burning ◽

North Atlantic ◽

Atmospheric Chemistry ◽

Fire History ◽

Fire Regime ◽

Ice Core ◽

North Atlantic Region ◽

Atlantic Region ◽

Ice Cap

Abstract. Biomass burning influences global atmospheric chemistry by releasing greenhouse gases and climate-forcing aerosols. There is controversy about the magnitude and timing of Holocene changes in biomass burning emissions from millennial to centennial timescales and, in particular, about the possible impact of ancient civilizations. Here we present a 5 kyr record of fire activity proxies levoglucosan, black carbon, and ammonium measured in the RECAP (Renland ice cap) ice core, drilled in coastal eastern Greenland, and therefore affected by processes occurring in the high North Atlantic region. Levoglucosan and ammonium fluxes are high from 5 to 4.5 kyr BP (thousand years before 2000 CE) followed by an abrupt decline, possibly due to monotonic decline in Northern Hemisphere summer insolation. Levoglucosan and black carbon show an abrupt decline at 1.1 kyr BP, suggesting a decline in the wildfire regime in Iceland due to the extensive land clearing caused by Viking colonizers. All fire proxies reach a minimum during the second half of the last century, after which levoglucosan and ammonium fluxes increase again, in particular over the last 200 years. We find that the fire regime reconstructed from RECAP fluxes seems mainly related to climatic changes; however over the last millennium human activities might have influenced wildfire frequency/occurrence substantially.

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Holocene History of Río Tranquilo Glacier, Monte San Lorenzo (47°S), Central Patagonia

Frontiers in Earth Science ◽

10.3389/feart.2021.813433 ◽

2021 ◽

Vol 9 ◽

Author(s):

Esteban A. Sagredo ◽

Scott A. Reynhout ◽

Michael R. Kaplan ◽

Juan C. Aravena ◽

Paola S. Araya ◽

...

Keyword(s):

Southern Hemisphere ◽

Northern Hemisphere ◽

Late Holocene ◽

Time Frame ◽

Ice Age ◽

European Alps ◽

Mountain Glacier ◽

The Holocene ◽

San Lorenzo ◽

Southern Patagonia

The causes underlying Holocene glacier fluctuations remain elusive, despite decades of research efforts. Cosmogenic nuclide dating has allowed systematic study and thus improved knowledge of glacier-climate dynamics during this time frame, in part by filling in geographical gaps in both hemispheres. Here we present a new comprehensive Holocene moraine chronology from Mt. San Lorenzo (47°S) in central Patagonia, Southern Hemisphere. Twenty-four new 10Be ages, together with three published ages, indicate that the Río Tranquilo glacier approached its Holocene maximum position sometime, or possibly on multiple occasions, between 9,860 ± 180 and 6,730 ± 130 years. This event(s) was followed by a sequence of slightly smaller advances at 5,750 ± 220, 4,290 ± 100 (?), 3,490 ± 140, 1,440 ± 60, between 670 ± 20 and 430 ± 20, and at 390 ± 10 years ago. The Tranquilo record documents centennial to millennial-scale glacier advances throughout the Holocene, and is consistent with recent glacier chronologies from central and southern Patagonia. This pattern correlates well with that of multiple moraine-building events with slightly decreasing net extent, as is observed at other sites in the Southern Hemisphere (i.e., Patagonia, New Zealand and Antarctic Peninsula) throughout the early, middle and late Holocene. This is in stark contrast to the typical Holocene mountain glacier pattern in the Northern Hemisphere, as documented in the European Alps, Scandinavia and Canada, where small glaciers in the early-to-mid Holocene gave way to more-extensive glacier advances during the late Holocene, culminating in the Little Ice Age expansion. We posit that this past asymmetry between the Southern and Northern hemisphere glacier patterns is due to natural forcing that has been recently overwhelmed by anthropogenic greenhouse gas driven warming, which is causing interhemispherically synchronized glacier retreat unprecedented during the Holocene.

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Extratropical Southern Hemisphere Synchronous Pressure Variability in the Early 20th Century

Journal of Climate ◽

10.1175/jcli-d-20-0498 ◽

2021 ◽

pp. 1-41

Author(s):

Ryan L. Fogt ◽

Charlotte J. Connolly

Keyword(s):

Southern Hemisphere ◽

Historical Data ◽

Austral Summer ◽

Southern Annular Mode ◽

Early 20Th Century ◽

Annular Mode ◽

Tropical Variability ◽

Zonal Wavenumber ◽

Meteorological Observations ◽

Statistical Relationships

AbstractBecause continuous meteorological observations across Antarctica did not start until the middle of the 20th century, little is known about the full spatial pattern of pressure variability across the extratropical Southern Hemisphere (SH) in the early 20th century, defined here as the period from 1905-1956. To fill this gap, this study analyzes pressure observations across the SH in conjunction with seasonal pressure reconstructions across Antarctica, which are based on observed station-to-station statistical relationships between pressure over Antarctica and the southern midlatitudes. Using this newly generated dataset, it is found that the early 20th century is characterized by synchronous, but opposite signed pressure relationships between Antarctica and the SH midlatitudes, especially in austral summer and autumn. The synchronous pressure relationships are consistent with the Southern Annular Mode, extending its well-known influence on SH extratropical pressure since 1957 into the early 20th century. Apart from connections with the Southern Annular Mode, regional and shorter-duration pressure trends are found to be associated with influences from tropical variability and potentially the zonal wavenumber three pattern. Although the reduced network of SH observations and Antarctic reconstruction capture the Southern Annular Mode in the early 20th century, reanalyses products show varying skill in reproducing trends and variability, especially over the oceans and high southern latitudes prior to 1957, which stresses the importance of continual efforts of historical data rescue in data sparse regions to improve their quality.

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