07 Sep 2022
07 Sep 2022
Status: a revised version of this preprint was accepted for the journal ACP.

Measurement Report: Understanding the seasonal cycle of Southern Ocean aerosols

Ruhi S. Humphries1,2, Melita D. Keywood1,2, Jason P. Ward1, James Harnwell1, Simon P. Alexander3,2, Andrew R. Klekociuk3,2, Keiichiro Hara4, Ian M. McRobert5, Alain Protat6,2, Joel Alroe7, Luke T. Cravigan7, Branka Miljevic7, Zoran D. Ristovski7, Robyn Schofield8, Stephen R. Wilson9, Connor J. Flynn10, Gourihar R. Kulkarni11, Gerald G. Mace12, Greg M. McFarquhar13, Scott D. Chambers14, Alastair G. Williams14, and Alan D. Griffiths14 Ruhi S. Humphries et al.
  • 1Climate Science Centre, CSIRO Oceans and Atmosphere, Melbourne, Australia
  • 2Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  • 3Australian Antarctic Division, Channel Highway, Kingston, Tasmania, Australia
  • 4Department of Earth Science System, Faculty of Science, Fukuoka University, Jyonan, Fukuoka, Japan
  • 5Engineering and Technology Program, CSIRO National Collections and Marine Infrastructure, Hobart, Australia
  • 6Australian Bureau of Meteorology, Melbourne, Australia
  • 7School of Earth and Atmospheric Sciences, Queensland University of Technology, Brisbane, Australia
  • 8School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Parkville, Victoria, Australia
  • 9Centre for Atmospheric Chemistry, School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, New South Wales, Australia
  • 10School of Meteorology, University of Oklahoma, Norman, United States of America
  • 11Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, United States of America
  • 12Department of Atmospheric Science, University of Utah, Salt Lake City, United States of America
  • 13Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Norman, United States of America
  • 14Environmental Research, ANSTO, Lucas Heights, New South Wales, Australia

Abstract. The remoteness and extreme conditions of the Southern Ocean and Antarctic region have meant that observations in this region are rare, and typically restricted to summertime during research or resupply voyages. Observations of aerosols outside of the summer season are typically limited to long-term stations, such as Kennaook/Cape Grim (KCG, 40.7° S, 144.7° E) which is situated in the northern latitudes of the Southern Ocean, and Antarctic research stations, such as the Japanese operated Syowa (SYO, 69.0° S, 39.6° E). Measurements in the mid-latitudes of the Southern Ocean are important, particularly in light of recent observations that highlighted the latitudinal gradient that exists across the region in summertime. Here we present two years (March 2016–March 2018) of observations from Macquarie Island (MQI, 54.5° S, 159.0° E) of aerosol (condensation nuclei larger than 10 nm, CN10) and cloud condensation nuclei (CCN at various supersaturations) concentrations. This important multi-year data set is characterised, and its features are compared with the long-term data sets from KCG and SYO together with those from recent, regionally relevant voyages. CN10 concentrations were the highest at KCG by a factor of ∼50 % across all non-winter seasons compared to the other two stations which were similar (summer medians of 530 cm-3, 426 cm-3 and 468 cm-3 at KCG, MQI and SYO, respectively). In wintertime, seasonal minima at KCG and MQI were similar (142 cm-3 and 152 cm-3, respectively), with SYO being distinctly lower (87 cm-3), likely the result of the reduction in sea spray aerosol generation due to the sea-ice ocean cover around the site. CN10 seasonal maxima were observed at the stations at different times of year, with KCG and MQI exhibiting January maxima and SYO having a distinct February high. Comparison of CCN0.5 data between KCG and MQI showed similar overall trends with summertime maxima and wintertime minima, however KCG exhibited slightly (∼10 %) higher concentrations in summer (medians of 158 cm-3 and 145 cm-3, respectively), whereas KCG showed ∼40 % lower concentrations than MQI in winter (medians of 57 cm-3 and 92 cm-3, respectively). Spatial and temporal trends in the data were analysed further by contrasting data to coincident observations that occurred aboard several voyages of the RSV Aurora Australis and the RV Investigator. Results from this study are important for validating and improving our models, highlight the heterogeneity of this pristine region, and the need for further long-term observations that capture the seasonal cycles.

Ruhi S. Humphries et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-568', Anonymous Referee #1, 13 Oct 2022
  • RC2: 'Comment on acp-2022-568', Anonymous Referee #2, 18 Nov 2022
  • AC1: 'Comment on acp-2022-568', Ruhi Humphries, 17 Jan 2023

Ruhi S. Humphries et al.

Data sets

Particle number concentrations at Kennaook/Cape Grim Keywood, M., Ward, J., Gras, J.

Atmospheric aerosol and Cloud Condensation Nuclei concentrations from Macquarie Island from 2016 to 2018 Humphries, Ruhi S., Ward, J., Keywood, M. D., & Alexander, S. P.

CAPRICORN2 - Atmospheric aerosol measurements from the RV Investigator voyage IN2018_V01 Humphries, Ruhi S., McRobert, I. M., Ward, J., Harnwell, J., & Keywood, M. D.

Aerosol Properties, Cold Water Trial voyage (IN2015_E01): CN3 and CCN Humphries, Ruhi S., Alroe, J., Ward, J. D., Keywood, M. D., McRobert, I. M., Cravigan, L. T., & Ristovski, Z. D.

Aerosol Properties, Ice-edge to Equator voyage (IN2016_V03): CN3 and CCN Humphries, Ruhi S., Alroe, J., Ristovski, Z. D., Keywood, M. D., Ward, J. D., McRobert, I. M., Cravigan, L. T., & Brown, R.

In-situ total aerosol number using condensation particle counters as observed during the SIPEX II voyage of the Aurora Australis, 2012 Humphries, R. S., Wilson, S. R., Keywood, M. D., Ward, J., & Schofield, R.

RV Investigator BOM Atmospheric Data Overview (2016 onwards) Protat, A., & Humphries, R. S.

Antarctic aerosol CN Hara, Keiichiro

MARCUS ARM CN and CCN data reprocessed to remove ship exhaust influence Humphries, Ruhi S.

Polar Cell Aerosol Nucleation - atmospheric measurements from the RV Investigator voyage IN2017_V01 Humphries, Ruhi S., Simmons, J. B., McRobert, I. M., Ward, J., Keywood, M. D., Chambers, S. D., Griffiths, A. D., Williams, A. G., & Wilson, S. R.

Ruhi S. Humphries et al.


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Short summary
Observations of aerosols in pristine regions are rare, but are vital to constraining the natural baseline from which climate simulations are calculated. Here we present recent seasonal observations of aerosols from the Southern Ocean and contrast them with measurements from Antarctica, Australia, and regionally relevant voyages. Strong seasonal cycles persist, but striking differences occur at different latitudes. This study highlights the need for more long-term observations in remote regions.