ThompsonThomp Lab Reconstructing westerly wind bursts from Abaiang coral using a Mn/Ca proxy TropicalTr o p ic Climate & Coral Reefs Zoe Benson1, Alice Chapman1, Diane Thompson1, Jess Carilli2, Tom Marchitto3, Hussein Sayani4, Kim Cobb4 1 Department of Geoscience, University of Arizona; 2 Scripps Institute of Oceanography; 3 University of Colorado, Boulder; 4 Georgia Institute of Technology
Background Coral Mn/Ca Trade Wind Mechanism Figure 4. • Zonal wind patterns inform near-term climate predictions1 1. Trade winds carry Mn- • However, equatorial Pacific wind records only span the past 30-40 years2 laden dust to Abaiang 2. Dust settles in lagoons 3, 4 • Mn/Ca ratios in coral can extend this record and adsorbs to sinking • Mn/Ca spikes are linked to WWB at Butaritari and Kiritimati5 particles 3. Mn particle Figure 1. 20th century sedimentation occurs reanalysis 2-month 4. Mn reduces to Mn2+ smoothed zonal wind 5. WWBs remobilize anomalies for Kiritimati a Mn2+, which then and Butaritari, compared integrates into coral with 1-year-lagged Mn/Ca record of two skeletons Kiritimati corals (green) and two Butaritari corals Strong El Niño Very strong El Niño a 8 (purple)5. Vertical gray More WWB 6 bands represent El Niño a Methods Results 4
years. Reproduced from 2 1. Coral core slabbed to 6-mm Figure 6a. Surface A. Chapman. 0
zonal wind -2
thickness NOAA Zonal Wind [m/s]
measurements at -4
2. Transect plotted along the Winds Zonal NOAA b Abaiang from 1949- -6 Fewer WWB maximum growth axis -8 2021. Strong 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030 ABG-11 Time Depth (mm) Top of coral (orange) and very b 185 180 175 170 165 160 155 150 145 140 135 Abaiang Site ABG-13 3. Slab milled along transect 1.2 8.4 1.25 8.6 strong (red) El Niño 1.3 4. Coral powder acidified 1.35 8.8 1.4 • events marked. 1.45 9 Abaiang lies in the path 1.5 9.2 1.55 Li/Mg 5. Major, minor, trace element 1.2 ABG-11 1.6 Sr/Ca 9.4
Li/Mg (mmol/mol) 1.65 of low-level easterly Possibly 1997-1998 El Niño event (mmol/mol) Sr/Ca b ratios analyzed via ICP-MS Figure 6b, 6c. 1.7 9.6 Li/Mg and Sr/Ca Depth (mm) Top of coral winds and has many c 190 185 180 175 170 165 160 155 150 145 1 8.9 ratios for coral 1.2 9 9.1 small channel openings 1.4 Possibly 1997-1998 Figure 5a, 5b. cores ABG-11 (b) El Niño event 9.2 1.6 9.3 1.8 Li/Mg to its west-facing Coral slab is c and ABG-13 (c). 9.4 ABG-13 Sr/Ca 2.0 9.5 Sr/Ca (mmol/mol) Sr/Ca
mounted to drill, Li/Mg (mmol/mol) lagoon Possible locations 2.2 9.6 then milled along of 1997-1998 El Westerly wind bursts d Depth (mm) Top of coral • Abaiang experiences planned transect. Variability in Mn/Ca ratio Niño event Possibly 1997-1998 El Niño WWBs during El Niño Figure 5c. Milled indicated. ABG-11 events coral core. a Mn/Ca (nmol/mol) d Fig 6d, 6e. Mn/Ca e Depth (mm) Top of coral Abaiang Fig 5d. Milled coral ratios for ABG-11 Figure 2. Satellite image of Abaiang coral sampling sites. core under light box (d) and ABG-13 (e). No variability in Mn/Ca
Weaker trade winds to show growth ABG-13
Mn/Ca (nmol/mol) No peak corresponding More WWB bands. to possible El Niño b Discussion and Future Work Acknowledgments • Abaiang corals have significantly lower Mn/Ca ratios than Kiritimati and Butaritari corals This work was funded by NSF-AGS-1931242 and the George Kiritimati H. Davis Undergraduate Research Fund. I would like to thank Butaritari • Abaiang Mn/Ca, Li/Mg, and Sr/Ca variability in Abaiang corals suggests they capture the 1997-1998 El Niño Alice and Sophia for their help milling, as well as Dr. Thompson • More sheltered sites (ABG-11) have higher Mn/Ca ratios than sites at channel openings (ABG-13) for all her guidance and help with data processing. • Future work: References Stronger trade winds • Run remaining ABG-13 samples in ICP-MS 1 England, M.H. et al. 2014. Nature Climate Change 4:222-2227 Fewer WWB 2 Chiodi, A.M. and D.E. Harrison. 2017. J Clim 30:1041-1059 • Mill ABG-10, then compare Mn/Ca ratios of ABG-13, ABG-10, and ABG-11 3 Shen, G.T. et al. 1992. JGR 97:12689-12697 • 4 Thompson, D.M. et al. 2014. Nature Geoscience 8:117-121 Figure 3. Global zonal wind anomalies at the surface during the 1997-1998 El Niño Event. Expand the Abaiang Mn/Ca coral record beyond the bounds of recorded wind observations 5 Sayani, H.R. et al. 2021. G-Cubed 22:1-12