Study Notes on Temperature Modulation of Northern Mid-Latitude Westerly Winds

Temperature Modulation of Northern Mid-Latitude Westerly Winds Intensity and Displacement across the Warm Pliocene

Authors and Affiliation

  • Ting Chen

    • Chongqing Key Laboratory of Carbon Cycle and Carbon Regulation of Mountain Ecosystem, Chongqing Normal University, Chongqing 401331, People’s Republic of China

  • Qingsong Liu

    • Centre for Marine Magnetism (CM2), Department of Ocean Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen 518055, People’s Republic of China

  • Hong Ao

    • Laboratory for Marine Geology, Laoshan Laboratory, Qingdao 266061, People’s Republic of China

    • State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, People’s Republic of China

  • David B. Ryves

    • Geography and Environment, Loughborough University, Loughborough LE11 3TU, UK

Article Information

  • Editor: Fabienne Marret-Davies

  • Keywords:

    • Late Miocene Asian aeolian dust

    • North Pacific Ocean

    • Diatoms

  • Publication Details: Global and Planetary Change

  • Received: 28 February 2024

  • Revised: 23 July 2024

  • Accepted: 24 July 2024

Abstract

  • The study investigates the variations of Northern Hemisphere Mid-latitude Westerly winds (NHMW) from 6.5 to 2.5 Ma using sediment core data.

  • Findings suggest NHMW underwent a northward shift and weakening from ~5.8 to 4.4 Ma, followed by strengthening and equatorward shift after ~4.4 Ma.

  • NHMW dynamics are critically linked to sea surface temperature gradients and the intensity of the Asian Summer Monsoon (ASM), with implications for future global climate change assessments.

1. Introduction

  • Pliocene Epoch Timeframe: 5.33 to 2.58 Ma; an important era for understanding future climates due to similar atmospheric CO2 levels (350–450 ppm) and global temperature approximately 3°C higher than pre-industrial levels.

  • Geographic Configuration:

    • Similar to today with limited Northern Hemisphere glaciation, and sea levels 10–30 meters higher than today.

  • Understanding climatic dynamics during this epoch helps refine future warming projections.

  • Westerly Winds Definition: Prevailing winds from west to east in mid-latitudes, crucial for atmosphere-ocean dynamics.

  • NHMW Impact:

    • Influences hydroclimate in Europe, central Asia, North America, and oceanic carbon exchanges.

2. Materials and Methods

2.1. Sampling and Age-Depth Models

  • Collected ~200 sediment subsamples at ~10 cm intervals from ODP Site 885.

  • Used X-ray fluorescence (XRF) for elemental analysis and diatom composition analysis on alternate samples.

  • Developed an age-depth model using palaeomagnetic reversals based on references.

2.2. Diatom Species Identification

  • Utilized a water bath method for sample preparation and mounted on glass slides.

  • Diatoms were identified using a phase-contrast light microscope, with a focus on at least 200 diatom valves per sample.

  • Conducted cluster analysis with Tilia software to determine diatom composition zones.

2.3. X-Ray Fluorescence Measurements

  • Analyzed powdered sediment samples using a WD-XRF spectrometer to determine bulk element concentrations and chemical indices.

  • Calculated Chemical Index of Alteration (CIA) and Rb/Sr ratio as indicators of chemical weathering intensity.

2.4. Grain Size Analyses

  • Performed on ~113 sediment samples, determining the mean size of aeolian dust using specific formulas to characterize dust at the site.

2.5. Calculation of Sea Surface Temperature Gradient

  • Utilized SST data from several IODP and ODP sites to calculate the gradient across latitudes, applying smoothing techniques for data analysis.

3. Results and Discussion

3.1. Position Shift of NHMW from the Late Miocene to the Late Pliocene

  • Dominant diatom species: Coscinodiscus marginatus, Neodenticula kamtschatica, and Thalassionema nitzschioides, accounting for over 77% of abundance.

  • Identified five statistically distinct zones for study analysis over the 6.5–2.5 Ma interval based on changes in diatom species.

  • Shift in diatom assemblages indicates northward shift of NHMW coinciding with temperature variations.

3.2. Strength Variations of NHMW and Humidity Condition in Central Asia

  • Observed that aeolian dust grain size indicates fluctuations in NHMW strength with observed patterns continuing through significant climatic shifts.

  • CIA and Rb/Sr ratios indicate periods of aridity and increased humidity corresponding to changes in NHMW dynamics.

3.3. Dynamics and Significance of Changes in NHMW

  • The correlation between NHMW patterns and temperature gradients impacting the ASM and related climatic events was highlighted.

  • The study proposes that NHMW dynamics significantly affect regional rainfall patterns and climate systems, leading to major regional implications as climate changes.

4. Conclusions

  • Provided detailed patterns in NHMW dynamics and humidity changes from 6.5–2.5 Ma, indicating a decrease in temperature gradients leading to NHMW weakening and enhances ASM. Future warming scenarios suggest NHMW may again shift, affecting central Asian hydroclimate. This paper looks at how the Northern Hemisphere Mid-latitude Westerly winds (NHMW) changed between 6.5 and 2.5 million years ago, a period called the Pliocene. This era is important because its climate conditions, like CO2 levels and global temperatures, were similar to what we might see in the future. The researchers discovered that these winds first moved northward and weakened (around 5.8 to 4.4 million years ago) and then strengthened and moved back towards the equator (after 4.4 million years ago). They found a critical connection between these wind changes, sea surface temperatures, and the strength of the Asian Summer Monsoon. Regarding humidity, the study specifically found that these shifts in the NHMW were linked to periods of dryness (aridity) and increased wetness (humidity) in Central Asia. By analyzing chemical markers in sediment samples (like CIA and Rb/Sr ratios), they could tell when the region was more arid or more humid, and these changes corresponded with the way the westerly winds were behaving. The paper concludes that understanding these wind dynamics is crucial because they significantly impact regional rainfall patterns and the overall climate, especially when considering future global warming scenarios that might cause similar shifts.

CRediT Authorship Contribution Statement

  • Contributions to the study from all authors were noted, with various roles in the writing, methodology, investigation, and funding acquisition.

Declaration of Competing Interest

  • Authors declare no competing interests.

Data Availability

  • Data available upon request.

Acknowledgements

  • Study funded by various scientific grants from national bodies in China.

References

  • Detailed citations of studies referred to throughout the text, covering various aspects of NHMW dynamics, climate change impacts, and historical geological data.