Influence of solar activity on climate : Poles to Tropics

Solar activities are directly or indirectly responsible for climate variability around the globe. Evidences of such correspondences between solar activities and palaeoclimatic proxy data have been reported from polar as well as tropical regions, suggesting solar influence over climate dynamics. However, these findings need to be further strengthened by covering vast geographical region for generating palaeoclimatic data and corresponding variations in solar activities. A better time control on proxy data is essential to arrive at conclusive understanding and plausible causal linkages between solar activity and climate changes from poles to tropics.

The Early Paleogene Succession at Tora, New Zealand; Stratigraphy and Paeloclimate: A Critical North Island Eocene Temperature Record and a Crucial Linkage Between the Depositional Settings of the Central and Southern East Coast Basin

<p>This study has utilised the Mg/Ca paleothermometry method to provide a new, North Island reference of sea temperatures in the Southwest Pacific during a period of extreme global warming, referred to as the Early Eocene Climatic Optimum (EECO; ~53-50 Ma). This period of Earth’s history is of great interest as it represents the warmest climates of the Cenozoic. Importantly the climate dynamics of this period as simulated by computer models do not appear to match paleo-proxy data, specifically with regard to the latitudinal distribution of heat. Development of this paleoceanographic record involved detailed mapping of three sections in the Wairarapa region (41.506199 S, 175.517663 E) of New Zealand’s North Island. Three primary stratigraphic sections (Pukemuri, Awheaiti and Te Oroi Streams) were described and dated using foraminiferal and calcareous nannofossil biostratigraphy, with supplementary observations and measurements included from sections at Manurewa and Te Kaukau Points. These sediments are primarily siliciclastic sandstones and mudstones in composition, and sedimentary structures within these sections include turbidite sequences, channelisation and synsedimentary slumping, suggesting the EECO interval here is represented by sedimentation within a mid-bathyal submarine channel and fan environment. In contrast, the Early Paleocene Manurewa and Awhea Formations have previously been interpreted as a shallow, marginal marine environment which is at odds with benthic foraminiferal paleodepth indicators and trace fossil assemblages identified in this study. Selected genera of planktic foraminifera were extracted from the EECO interval and paleo-water temperatures determined from Mg/Ca values measured by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICPMS). This method was selected as it allows specific targeting of analysis sites, enabling avoidance of contaminated and altered parts of the test. This method also provides simultaneous measurements of other trace elements (Al, Si, Ti, Mn, Zn, Sr, Ba) that can be used as a guide to preservation state of the test (for example, Al, Ti and Si are considered indicators of detrital contamination levels). Four foraminifera genera were selected as suitable paleotemperature indicators of separate components of the water column. Morozovella spp. and Acarinina spp. were selected for surface mixed layer paleotemperature estimates, Subbotina spp. for thermocline temperature values, and Cibicides spp. for bottom water temperature determinations.SEM images, combined with trace element data were used to parse the resulting Mg/Ca data and only those that met strict quality criterion, including low detrital contamination and lack of visual evidence for recrystalisation were used for temperature reconstruction. Planktic Mg/Ca data were converted to temperature using the relationship (Mg/Ca = [Mg/Casw-t]/[Mg/Casw-0] × 0.38 0.09 × T) and benthic Mg/Ca temperatures calculated using (Mg/Ca = [Mg/Casw-t]/[Mg/Casw-0] × 0.87 0.109 × T), each assuming an early Eocene seawater Mg/Ca value of 4.1 mol/mol. Calibrated Mg/Ca results show peak sea surface temperatures of 29°C for Morozovella and Acarinina in the East Coast Basin during the Early Eocene, with bottom water temperatures of 17°C obtained from Cibicides. These data are consistent with the high sea surface temperatures reconstructed by previous workers in the nearby Canterbury Basin. The data from this new reference point support the idea that the EECO was characterised by a lower, possibly absent latitudinal temperature gradient in the midlatitude Southwest Pacific, than numerical models suggest, indicating a fundamental gap in the knowledge of climate dynamics in conditions much warmer than today.</p>

The Early Paleogene Succession at Tora, New Zealand; Stratigraphy and Paeloclimate: A Critical North Island Eocene Temperature Record and a Crucial Linkage Between the Depositional Settings of the Central and Southern East Coast Basin

<p>This study has utilised the Mg/Ca paleothermometry method to provide a new, North Island reference of sea temperatures in the Southwest Pacific during a period of extreme global warming, referred to as the Early Eocene Climatic Optimum (EECO; ~53-50 Ma). This period of Earth’s history is of great interest as it represents the warmest climates of the Cenozoic. Importantly the climate dynamics of this period as simulated by computer models do not appear to match paleo-proxy data, specifically with regard to the latitudinal distribution of heat. Development of this paleoceanographic record involved detailed mapping of three sections in the Wairarapa region (41.506199 S, 175.517663 E) of New Zealand’s North Island. Three primary stratigraphic sections (Pukemuri, Awheaiti and Te Oroi Streams) were described and dated using foraminiferal and calcareous nannofossil biostratigraphy, with supplementary observations and measurements included from sections at Manurewa and Te Kaukau Points. These sediments are primarily siliciclastic sandstones and mudstones in composition, and sedimentary structures within these sections include turbidite sequences, channelisation and synsedimentary slumping, suggesting the EECO interval here is represented by sedimentation within a mid-bathyal submarine channel and fan environment. In contrast, the Early Paleocene Manurewa and Awhea Formations have previously been interpreted as a shallow, marginal marine environment which is at odds with benthic foraminiferal paleodepth indicators and trace fossil assemblages identified in this study. Selected genera of planktic foraminifera were extracted from the EECO interval and paleo-water temperatures determined from Mg/Ca values measured by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICPMS). This method was selected as it allows specific targeting of analysis sites, enabling avoidance of contaminated and altered parts of the test. This method also provides simultaneous measurements of other trace elements (Al, Si, Ti, Mn, Zn, Sr, Ba) that can be used as a guide to preservation state of the test (for example, Al, Ti and Si are considered indicators of detrital contamination levels). Four foraminifera genera were selected as suitable paleotemperature indicators of separate components of the water column. Morozovella spp. and Acarinina spp. were selected for surface mixed layer paleotemperature estimates, Subbotina spp. for thermocline temperature values, and Cibicides spp. for bottom water temperature determinations.SEM images, combined with trace element data were used to parse the resulting Mg/Ca data and only those that met strict quality criterion, including low detrital contamination and lack of visual evidence for recrystalisation were used for temperature reconstruction. Planktic Mg/Ca data were converted to temperature using the relationship (Mg/Ca = [Mg/Casw-t]/[Mg/Casw-0] × 0.38 0.09 × T) and benthic Mg/Ca temperatures calculated using (Mg/Ca = [Mg/Casw-t]/[Mg/Casw-0] × 0.87 0.109 × T), each assuming an early Eocene seawater Mg/Ca value of 4.1 mol/mol. Calibrated Mg/Ca results show peak sea surface temperatures of 29°C for Morozovella and Acarinina in the East Coast Basin during the Early Eocene, with bottom water temperatures of 17°C obtained from Cibicides. These data are consistent with the high sea surface temperatures reconstructed by previous workers in the nearby Canterbury Basin. The data from this new reference point support the idea that the EECO was characterised by a lower, possibly absent latitudinal temperature gradient in the midlatitude Southwest Pacific, than numerical models suggest, indicating a fundamental gap in the knowledge of climate dynamics in conditions much warmer than today.</p>

Spectral analysis of climate dynamics with operator-theoretic approaches

The Earth’s climate system is a classical example of a multiscale, multiphysics dynamical system with an extremely large number of active degrees of freedom, exhibiting variability on scales ranging from micrometers and seconds in cloud microphysics, to thousands of kilometers and centuries in ocean dynamics. Yet, despite this dynamical complexity, climate dynamics is known to exhibit coherent modes of variability. A primary example is the El Niño Southern Oscillation (ENSO), the dominant mode of interannual (3–5 yr) variability in the climate system. The objective and robust characterization of this and other important phenomena presents a long-standing challenge in Earth system science, the resolution of which would lead to improved scientific understanding and prediction of climate dynamics, as well as assessment of their impacts on human and natural systems. Here, we show that the spectral theory of dynamical systems, combined with techniques from data science, provides an effective means for extracting coherent modes of climate variability from high-dimensional model and observational data, requiring no frequency prefiltering, but recovering multiple timescales and their interactions. Lifecycle composites of ENSO are shown to improve upon results from conventional indices in terms of dynamical consistency and physical interpretability. In addition, the role of combination modes between ENSO and the annual cycle in ENSO diversity is elucidated.