1 Virginia Tech, Dept. of Geosciences, Blacksburg, VA

1. The Long-Term Variation of Short-Term Oceanographic Events Revealed by Stable Isotope Sclerochronology of Amino Acid Dated Bivalve and Brachiopod Shells Richard A. Krause Jr.1, Susan L. Barbour-Wood1, Christopher Romanek2, Michał Kowalewski1, Marcello G. Simões3, and John F. Wehmiller4 1 Virginia Tech, Dept. of Geosciences, Blacksburg, VA 2 Savannah River Ecological Laboratory, Univ. of Georgia, Aiken, SC 3 Instituto de Biociencias, Universidade Estadual Paulista, Botucatu, Brazil 4 Univ. of Delaware, Dept. of Geology, Newark, DE

2. South Brazil Current The South Brazilian Bight Marine Province is Dominated by the South Brazil Current. 0 CW TW 21°C 19°C 17°C 100 shelf profile 15°C 200 13°C Depth (m) Coastal water (CW) 300 SACW Tropical water (TW) 11°C South Atlantic Central Water (SACW) 400 500 50 km NW SE Santos Basin Coast The South Brazil Current is a weak western-boundary current that carries warm subtropical water south, along the Brazilian Coast. Present oceanographic conditions include seasonal coastal upwelling and non-seasonal freshwater runoff events (possibly linked to ENSO events). Kowalewski et al., 2002, Palaios Coastal Water: mean annual salinity = 33- 34‰ mean annual temp. = >20°C Tropical Water: mean annual salinity = 33- 34‰ mean annual temp. = >20°C South Atlantic Central Water: mean annual salinity = ~34- 35‰ mean annual temp. = <20°C

3. South Brazil Current How have these conditions fluctuated in the Holocene? 0 CW TW 21°C 19°C 17°C 100 shelf profile 15°C 200 13°C Depth (m) Coastal water (CW) 300 SACW Tropical water (TW) 11°C South Atlantic Central Water (SACW) 400 500 50 km NW SE Santos Basin Coast Kowalewski et al., 2002, Palaios Goals: To assess the long-term variation of short-term oceanographic events. 1) Seasonal Coastal Upwelling 2) ENSO related freshwater runoff events To understand the multi-centennial dynamics of ocean currents and marine bio-productivity.

4. Collections are from Ubatuba Bay, Southeast Brazilian Bight. • Shells collected as surficial bulk samples • Van Veen grabs and short dredges • Collection at multiple sites • This talk will focus on shells from inner shelf (10m site) • Research focused on 2 species • Semele casali • aragonitic bivalve • thin shell • infaunal • Bouchardia rosea • calcitic brachiopod • robust shell • epifaunal 10 mm Barbour-Wood et al., in review, Quaternary Research 10 mm

5. Methods: Amino Acid Racemization Dating Brachiopods (n = 90) 20 15 • Bouchardia rosea (Brachiopoda) r2=0.97 0.4 10 • Semele casali (Bivalvia) 5 0.3 0 Bivalves (n = 71) D/L Asp2 0.2 10 r2=0.86 0.1 5 0 0 0 1000 2000 3000 4000 5000 6000 7000 Calendar Years B.P. Barbour-Wood et al., in review, Quaternary Research 0 1000 2000 3000 4000 5000 6000 7000 8000 Calendar Years BP • D/L aspartic acid (D/L Asp) • Shells sampled from same region to minimize intra-shell variability (Carroll et al, 2003) • Racemization analysis performed on gas chromatograph with 25 m Chirasil-Val column and flame ionization detector. • D/L Asp ratios are excellent predictors of 14C age for both species Number of shells

6. Methods: Carbon and Oxygen Stable Isotopes Shell carbonate analyzed for carbon and oxygen isotopes using continuous flow isotope ratio mass spectrometry (CF-IRMS) High spatial resolution sampling accomplished with a computer controlled micro-milling system >Carbonate drilled from shells along transects parallel to external growth lines >Sampling resolution: every 200-400 μm Neither species exhibits an appreciable vital effect 1 mm 1 mm 1 mm

7. Possible short-term oceanographic patterns • Background Conditions: Coastal upwelling water masses and runoff water masses are absent. • Bottom Water dominated by: • Coastal Water (CW) on inner shelf • Tropical Water (TW) of SBC on mid shelf • South Atlantic Central Water (SACW) on outer shelf • Sea surface temperature (SST) shifting annually by no more than 6°C • Salinity varying by less than 1‰ South Brazil Current 0 CW TW 21°C 19°C 17°C 100 15°C shelf profile 200 13°C Depth (m) Coastal water (CW) 300 SACW Tropical water (TW) 11°C South Atlantic Central Water (SACW) 400 500 50 km NW SE Santos Basin Coast Kowalewski et al., 2002, Palaios

8. Possible short-term oceanographic patterns 0 CW TW 21°C 19°C 17°C 100 15°C 200 13°C Depth (m) Coastal water (CW) 300 SACW Tropical water (TW) 11°C South Atlantic Central Water (SACW) 400 500 50 km NW SE Santos Basin Coast Kowalewski et al., 2002, Palaios 2) Coastal Upwelling: Seasonal upwelling can become stronger as cyclonic meanders of the SBC coincide with wind-driven episodes of the offshore Ekman transport. Pronounced events occur intermittently in austral summers Result of such events: Inner shelf experiences seasonally elevated phytoplankton blooms associated with nutrient-rich waters (SACW) Salinity may increase slightly (~1‰) SST may drop notably (~6°C) South Brazil Current shelf profile

9. Possible short-term oceanographic patterns 0 CW TW 21°C 19°C 17°C 100 15°C 200 13°C Depth (m) Coastal water (CW) 300 SACW Tropical water (TW) 11°C South Atlantic Central Water (SACW) 400 500 50 km NW SE Santos Basin Coast Kowalewski et al., 2002, Palaios 3) Freshwater Runoff / ENSO: Cold, low salinity waters invade region intermittently from the south Events correlated with Southern Oscillation Index (SOI), and thus suggest an ENSO link Result of such events: Inner shelf experiences seasonally elevated phytoplankton blooms associated with nutrient-rich coastal runoff Salinity will drop markedly SST may drop slightly South Brazil Current shelf profile

10. Summary of physical characteristics of short-term events Change relative to background conditions Salinity Sea Surface Temp. Coastal Upwelling large decrease slight increase Freshwater Runoff large decrease slight decrease

11. What is the expected isotopic signature of each of the hypothesized patterns? 2.00 • Background Conditions δ13C: 1-2‰ (Hudson, 1977) δ18O: -1.3 to 2.2‰ (Schmidt et al, 1999) • Coastal Upwelling Decrease in δ13C from background Possible slight +/- excursion in δ18O • Freshwater Runoff / ENSO Decrease in δ13C from background Decrease in δ18O from background 1.00 0.00 δ18O -1.00 -2.00 -3.00 -4.00 -2.00 0.00 2.00 4.00 minimum δ13C value for each shell

12. What is the expected isotopic signature of each of the hypothesized patterns? Freshwater Runoff / ENSO Brachiopod 652 yrs. BP 3 2 2 1 δ13C 1 0 0 -1 -2 0 -1 δ18O -2 0 5 10 Background Conditions Coastal Upwelling Bivalve 2944 yrs. BP ?? δ13C 1 δ18O 0 0 5 10 Distance from hinge (mm)

13. δ13C range may be a reliable event-indicator. Age 0 2 1-300 301-600 601-900 >900 1 δ13C average 0 -1 0 1 2 3 4 5 6 δ13C range 3 2 1 δ13C 0 -1 -2 -3 -4 modern 1000 2000 3000 4000 5000 6000 7000 0 100 200 300 400 500 600 700 Years BP • As range increases, δ13C average drops. • Productivity events are often short-lived (captured within the 4-7yr lifetime of the organism). • This phenomenon seems to be time-invariant.

14. Selected δ13C profiles for the last 6000 years. 2 1 0 100 200 300 400 500 600 700 0 0 0 0 0 0 0 0 5 5 5 5 5 5 5 5 10 10 10 10 10 10 10 10 15 15 15 15 15 15 15 15 Brachiopods Bivalves 2 2 1 3 1 0 0 5 10 15 20 2 0 3 2 1 -1 1 2 1 2 0 -2 0 1 0 1 -3 -1 0 -1 0 -2 0 5 10 15 -2 0 5 10 2 -3 1 -4 0 2 3 2 1 2 2 1 0 1 1 0 0 5 10 0 0 0 5 10 15 1000 2000 3000 4000 5000 6000 7000 High / Variable Primary Productivity High / Variable Primary Productivity Relatively Stable; Background Conditions Relatively Stable; Background Conditions 3 2 δ13C 1 0 0 5 10 Years Before Present δ13C Distance from hinge (mm) Distance from hinge (mm) Distance from hinge (mm)

15. Future Research Rio de Janeiro Sao Paulo Ubatuba South America Analyze additional shells: >Coastal sites several sites; up to 30m >Outer-Shelf sites 101 additional sites 60-808m Analysis of trace elements (Mg, Mn, Sr, Ba) High-resolution sampling (LA-ICPMS) Allow better distinction between high-productivity events High productivity: High Ba content in shell carbonate Lower SST: Lower Sr content in shell carbonate

16. Conclusions 0 5 10 15 30 20 # of shells 10 1 0 2000 8000 4000 6000 0 Calendar Years BP -1 -2 -3 -4 • The Holocene history of short-term oceanographic events can be reconstructed using time series of surficially-collected invertebrate shells. • The Southeast Brazilian Bight seems to have been characterized by discrete periods of elevated or variable bio-productivity. • Amino-acid dated invertebrate shells can yield insight into Holocene climate and oceanographic patterns. • As such, time series shown here may expand the arsenal of long-term climatic and environmental proxies. δ13C Distance from hinge (mm)

18. 2 2 1 1 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 5 5 5 5 5 5 5 5 5 5 5 5 5 10 10 10 10 10 10 10 10 10 10 10 10 10 10 15 15 15 15 15 15 15 15 15 15 15 15 15 15 1 2 3 0 Brachiopods Bivalves 2 1 2 -1 2 1 0 1 -2 3 1 0 5 10 0 0 3 0 5 10 15 20 2 0 3 2 2 1 -1 1 2 2 1 1 2 0 -2 0 1 1 0 2 2 0 1 -3 -1 0 0 5 10 0 -1 1 1 0 -2 0 5 10 15 -2 0 0 0 5 10 2 -3 -1 1 -4 0 2 3 2 1 2 2 1 0 1 1 0 0 5 10 0 0 0 5 10 15 δ13C δ13C δ13C δ13C 1000 2000 3000 4000 5000 6000 7000 0 100 200 300 400 500 600 700 Years Before Present

19. What is the trace element signature for the hypothesized patterns? Barium: Elevated levels associated with areas of high productivity. Strontium: Widely used as a paleo-thermometer of sea-surface temperatures. Cooler temperatures cause a draw-down in Sr/Ca 5 4 δ13C range 3 2 • High-productivity events • upwelling or runoff • Cooler-temperature events • upwelling 1 3 2 δ18O range 1 5 10 15 1000 2000 Average Ba/Ca Average Sr/Ca