Alkaline earth metal isotopes as a novel tool to constrain water sources and changes in carbonate precipitation in the lagoon-estuarine environments
Y. (Mandy) Shao1,*, J. Farkaš1,2, L. Mosley3, J. Tyler1, H. Wong4, M. Samanta1, C. Holmden5, B. M.
Gillanders3, A. Kolevica6 and A. Eisenhauer6
1Department of Earth Sciences, University of Adelaide, Australia 2Department of Environmental Geosciences, Czech University of Life Sciences, Czech Republic3Department of Ecology and Evolutionary Biology, University of Adelaide, Australia4Australian Nuclear Science and Technology Organisation, Australia5Department of Earth Sciences, University of Saskatchewan, Canada6GEOMAR, Helmholtz Centre for Ocean Research Kiel, Germany
*correspondence: [email protected]
8th Nov. 2019
Past Modern/Future
Paleo-hydrology
Water source mixing
water cycle
water resources
environmental sustainability
Decision making
Tracers
(87Sr/86Sr,
δ88/86Sr)
Fossil shells
Refer back
Land-ocean interface
A broad picture…
• Climate change
• Anthropogenic (human)
disturbances
Alkaline earth metal elements??
Our Tools:
Strontium (Sr)
• 87Sr/86Sr – radiogenic
• 88Sr/86Sr – stable
The Coorong– a natural isotope laboratory
(Gillanders and Munro, 2012)
Lake
Alexandrina
N. Lagoon S. Lagoon
Hypersaline
Modified from Shao et al. (2018)
- Unique geomorphology and large salinity
gradient!
Sea-
water
Know the past for a better future…
• Problems of the wetland site
➢Difficulties in freshwater management
➢The Millennium Drought (late 90s to 2010)
➢Changes to ecological condition
➢Decreased tourism
• Murray-Darling Basin Plan: “$8 billion spent and still the Coorong wetland is dying”
• What was the past like? More saline or fresh?
Algae-covered ground at the South Lagoon
In this talk:
Water samples Shell samples
• Introduction to strontium isotope systems (87Sr/86Sr and δ88/86Sr)
• Application of strontium isotopes in the modern Coorong
➢Water source mixing and carbonate fluxes
➢The role of the South Coorong Lagoon as a sink of DIC – linked to blue carbon
• Application of strontium isotopes in paleo-hydrology studies
➢Calibration of δ88/86Sr against δ44/40Ca and salinity in the Coorong water
➢Calibration of δ88/86Sr in shells (A. helmsi) and local waters in the Coorong
➢87Sr/86Sr and δ88/86Sr in shells (A. helmsi) from a South Lagoon sediment core
Arthritica helmsi (aragonitic)(Chamberlayne, 2015)
Stable Strontium Isotope Systematics
Radiogenic Strontium Isotope (87Sr/86Sr) System
Tracer of radiogenic processes:
• Provenance identification
• Global weathering
• Water source mixing
Stable Strontium Isotope Systematics
Stable Strontium Isotope (88Sr/86Sr) System
d88/86Sr =
88Sr86Sr sample
88Sr86Sr standard
- 1 *103
Standard used: SRM/NBS987
Measured by TIMS with Double-Spike correction
• Sensitive to mass-dependent isotope fractionation processes
(e.g. carbonate precipitation/dissolution)
• ∆88/86Sr (δ88/86Srcarb- δ88/86Srwater) – independent of
environmental parameters (i.e., temperature, pH, salinity or
carbonate ion concentration) (Raddatz et al., 2013; Vollstaedt
et al., 2014; Fruchter et al., 2016)
• Good indicator of paleo-water Sr isotope signatures
The two-dimensional isotope tracers – 87Sr/86Sr and δ88/86Sr in the modern Coorong
• Major water components - fresh, brackish, marine and hypersaline
• 87Sr/86Sr – water source mixing
• δ88/86Sr – carbonate precipitation/dissolutionR
ad
iog
en
ic S
r is
oto
pe
ra
tio
Stable Sr isotope ratio
Carbonate fluxes in the Coorong – Saturation indices (SI) by PHREEQC
SI = 0 just saturated
SI > 0 supersaturated
SI < 0 undersaturated
Saturation Index (SI)
SI = Log
Carbonate precipitation in the Coorong – field evidence
(Haese et al., 2008)
Carbonate ‘tufa’
Policeman Point
Strand pools
Stony Well
Active seep showing
agitated sediment
south of Parnka Point
(Zeebe and Wolf-Gladrow, 2001)
The South Lagoon acts as an efficient sink of carbon
due to ongoing CaCO3 formation (mostly as aragonite)
Coorong δ88/86Sr vs δ44/40Ca and salinity
δ44/40Ca data extracted from Shao et al. (2018)
Fractionation of δ88/86Sr – biogenic carbonates (A. helmsishells) vs. water
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
35.59 35.6 35.61 35.62 35.63 35.64 35.65
δ8
8/8
6Sr
(‰
)
Latitude (S)
water
shells
∆88/86Sr (δ88/86Srcarb- δ88/86Srwater) = -0.09 ‰ (constant)
The basis of the paleo-hydrology reconstruction!
Arthritica helmsi
(aragonitic)(Chamberlayne, 2015)
Sampled by Ms. Deborah Haynes in 2005 and 2006.
Coring site C18
N. Lagoon S. Lagoon
Parnka Pt.
Age Model by C-14 dating
Coorong southern lagoon: Core C18
smooth spline 0.3
(Chamberlayne, 2015)
Salt Creek
C18
Paleo-hydrology of the Coorong
Sediment core C18
Fossil A. helmsi
• Gentle increasing trends
• ~600-year cycles?
• Has never been purely marine in the past 2500+ yrs
Age (years BP)
0.70916
0.70917
0.70918
0.70919
0.7092
0.70921
0.70922
0.70923
0.70924
0.70925
0.70926
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
0.48
0.50
0 10 20 30 40 50 60 70 80 90 100 110 120 130
87S
r/86S
r
δ88/8
6S
r (
‰)
Depth (cm)
Seawater
Seawater
Paleo-hydrology of the Coorong
Sediment core C18
Fossil A. helmsi
Increased continental influence, evaporation/salinity
and carbonate precipitation?
Summary
• Coupling 87Sr/86Sr and δ88/86Sr can constrain water mixing and carbonate precipitation/dissolution in the modern Coorong, also forms a two-dimensional tracers to understand the controlling processes of the local hydrology in the modern Coorong
• δ88/86Sr and mineral saturation modelling suggests that the South Lagoon acts as an efficient sink of carbon due to ongoing CaCO3 formation (mostly as aragonite)
• Similar fractionation behaviour in stable Sr and Ca isotopes (i.e, δ88/86Sr and δ44/40Ca) is confirmed, and results suggest systematic increasing trend of δ88/86Sr with salinity in the Coorong waters
• Fractionation between living A. helmsi shells and local water in the Coorong ∆88/86Sr (δ88/86Srcarb- δ88/86Srwater) = -0.09 ‰ (constant), forming the basis of paleo-hydrology reconstruction
• 87Sr/86Sr and δ88/86Sr in the A. helmsi shells from the sediment core C18 indicate more continental input and increasing carbonate precipitation in the South Lagoon since ~2000 yrs BP (more measurements to be done).
Acknowledgements
Dr. Juraj Farkaš Dr. Jonathan Tyler Prof. Bronwyn
Gillanders
Ms. Deborah
Haynes
Ms. Briony
Chamberlayne
Prof. Luke Mosley
• Adelaide Graduate
Research Scholarship
(AGRS)
• CRC LEME Regolith
Science Scholarship
• EU funding from Dr.
Juraj Farkaš
• Staff from the University
of AdelaideMr. David Bruce
Dr. Moneesha
Samanta
Dr. John Tibby
- The end ☺
Thank you for listening!!
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