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-Wood 1, Christopher Romanek 2, Michał Kowalewski 1, Marcello G. Simões 3, and John F. Wehmiller 4 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

The South Brazilian Bight Marine Province is Dominated by the South Brazil Current. SACW TW CW Coastal water (CW) Tropical water (TW) South Atlantic Central Water (SACW) 11°C 13°C 15°C 17°C 19°C 21°C NWSE Coast Santos Basin 50 km Depth (m) Kowalewski et al., 2002, Palaios 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). South Brazil Current shelf profile Coastal Water: mean annual salinity = ‰ mean annual temp. = >20°C Tropical Water: mean annual salinity = ‰ mean annual temp. = >20°C South Atlantic Central Water: mean annual salinity = ~34- 35‰ mean annual temp. = <20°C

How have these conditions fluctuated in the Holocene? SACW TW CW Coastal water (CW) Tropical water (TW) South Atlantic Central Water (SACW) 11°C 13°C 15°C 17°C 19°C 21°C NWSE Coast Santos Basin 50 km Depth (m) 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. South Brazil Current shelf profile

Barbour-Wood et al., in review, Quaternary Research 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

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 14 C age for both species Methods: Amino Acid Racemization Dating Calendar Years B.P. D/L Asp 2 -Bouchardia rosea (Brachiopoda) -Semele casali (Bivalvia) r 2 =0.97 r 2 =0.86 Barbour-Wood et al., in review, Quaternary Research Brachiopods (n = 90) Calendar Years BP Bivalves (n = 71) Number of shells

Methods: Carbon and Oxygen Stable Isotopes 1 mm 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 μm Neither species exhibits an appreciable vital effect

NWSE Coast Santos Basin SACW TW CW Coastal water (CW) Tropical water (TW) South Atlantic Central Water (SACW) 11°C 13°C 15°C 17°C 19°C 21°C 50 km Depth (m) Kowalewski et al., 2002, Palaios Possible short-term oceanographic patterns 1)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 shelf profile

NWSE Coast Santos Basin SACW TW CW Coastal water (CW) Tropical water (TW) South Atlantic Central Water (SACW) 11°C 13°C 15°C 17°C 19°C 21°C 50 km Depth (m) Kowalewski et al., 2002, Palaios Possible short-term oceanographic patterns 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

NWSE Coast Santos Basin SACW TW CW Coastal water (CW) Tropical water (TW) South Atlantic Central Water (SACW) 11°C 13°C 15°C 17°C 19°C 21°C 50 km Depth (m) Kowalewski et al., 2002, Palaios Possible short-term oceanographic patterns 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

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

 Background Conditions δ 13 C: 1-2‰ (Hudson, 1977) δ 18 O: -1.3 to 2.2‰ (Schmidt et al, 1999)  Coastal Upwelling Decrease in δ 13 C from background Possible slight +/- excursion in δ 18 O  Freshwater Runoff / ENSO Decrease in δ 13 C from background Decrease in δ 18 O from background What is the expected isotopic signature of each of the hypothesized patterns? minimum δ 13 C value for each shell δ 18 O 2.00

Bivalve 2944 yrs. BP δ 13 C δ 18 O δ 18 O Distance from hinge (mm) Background Conditions Brachiopod 652 yrs. BP δ 13 C Freshwater Runoff / ENSO Coastal Upwelling What is the expected isotopic signature of each of the hypothesized patterns? ??

modern Years BP δ 13 C δ 13 C range may be a reliable event-indicator δ 13 C average δ 13 C range >900 Age -As range increases, δ 13 C average drops. -Productivity events are often short-lived (captured within the 4-7yr lifetime of the organism). - This phenomenon seems to be time- invariant.

Years Before Present δ 13 C δ 13 C Brachiopods Bivalves Selected δ 13 C profiles for the last 6000 years. Distance from hinge (mm) High / Variable Primary Productivity Relatively Stable; Background Conditions High / Variable Primary Productivity Relatively Stable; Background Conditions

Future Research Sao Paulo South America Rio de Janeiro Ubatuba Analyze additional shells: >Coastal sites several sites; up to 30m >Outer-Shelf sites 101 additional sites m 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

Conclusions 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 # of shells Calendar Years BP δ 13 C Distance from hinge (mm)

Years Before Present δ 13 C δ 13 C Brachiopods Bivalves

Average Sr/Ca Average Ba/Ca δ 13 C range δ 18 O range 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  High-productivity events  upwelling or runoff  Cooler-temperature events  upwelling