Uranium, Thorium and Protactinium isotopes of ODP Site 172-1063

Ocean circulation may have undergone reductions and reinvigorations in the past closely tied to regional climate changes. Measurements of 231Pa/230Th ratios in a sediment core from the Bermuda Rise have been interpreted as evidence that the Atlantic Meridional Overturning Circulation (AMOC) was weakened or completely eliminated during a period of catastrophic iceberg discharges (Heinrich-Event 1, H1). Here we present new data from the Bermuda Rise that show further 231Pa/230Th peaks during Heinrich-2 (H2) and Heinrich-3 (H3). Additionally, a tight correlation between diatom abundances (biogenic silica) and 231Pa/230Th is discovered in this core. Our results redirect the interpretation of 231Pa/230Th from the Bermuda Rise as a proxy for ocean circulation towards a proxy that reacts highly sensitive to changes of particle composition and water mass properties.

Atlantic 231Pa/230Th and biogenic opal compilation of the Holocene and the LGM

The strength and geometry of the Atlantic meridional overturning circulation is tightly coupled to climate on glacial-interglacial and millennial timescales, but has proved difficult to reconstruct, particularly for the Last Glacial Maximum. Today, the return flow from the northern North Atlantic to lower latitudes associated with the Atlantic meridional overturning circulation reaches down to approximately 4,000 m. In contrast, during the Last Glacial Maximum this return flow is thought to have occurred primarily at shallower depths. Measurements of sedimentary 231Pa/230Th have been used to reconstruct the strength of circulation in the North Atlantic Ocean, but the effects of biogenic silica on 231Pa/230Th-based estimates remain controversial. Here we use measurements of 231Pa/230Th ratios and biogenic silica in Holocene-aged Atlantic sediments and simulations with a two-dimensional scavenging model to demonstrate that the geometry and strength of the Atlantic meridional overturning circulation are the primary controls of 231Pa/230Th ratios in modern Atlantic sediments. For the glacial maximum, a simulation of Atlantic overturning with a shallow, but vigorous circulation and bulk water transport at around 2,000 m depth best matched observed glacial Atlantic 231Pa/230Th values. We estimate that the transport of intermediate water during the Last Glacial Maximum was at least as strong as deep water transport today.

U-M Softball Team, 1978

Front Row: Manager Debbie Snyder, Diane Mettelman, Tammy Herremans, Debbie Allor, Anna Bullard, Theresa Gardocki, Head Coach Gloria Soluk

Second Row: Shelly Piilo, Evelyn Edgecombe, Ann Slade, Kathy VanDeusen, Katy Brady, Sheryl Tominac, Trainer Laura Pieri

Top Row: Brenda Venhuizen, Mary Hibbard, Terry Conlin, Theresa Wyckoff, Roberta Zald, Fran Wiecha, Ass't. Coach Mina Sonda

U-M Softball Team, 1982

Back Row: Head Coach Bob DeCarolis, Assistant Coach Sam Holtz, Co-Captain Laura Reed, Co-Captain Diane Hatch, Trainer Sue Peel, Assistant Coach Mike Briguglio

Middle Row: Mena Reyman, Lisa Panetta, Julie Galletti, Karen Crawfis, Tammie Sanders, Jody Humphries, Sandy Taylor

Front Row: Debbie Haines, Jan Boyd, Marcie Smith, Sue Burk, Mary Bitkowski, Karen Pollard, Missy Thomas

University of Michigan Field Hockey Team, 1986

Front Row: trainer Kim Godek, manager Cheryl Mick, Sara Clark, Sharon Cantor, Diane Pentaleri, Lisa Murray, Joan Taylor, Andrea Kuebbeler, Margaret Kundtz, Ilene Meadows, assistant coach Andrea Wickerham;

Back Row: head trainer Sue Peel, Gillian Pieper, Jane Nixon, Debbie Devine, Judy Burinskas, Patti Farley, Trisha Mondul, Katrina Warner, Tracy Gaskins, Dorie McCubbrey, Robin Ives, Maryann Bell, Head Coach Karen Collins.

(Not pictured: Joanne Green)

University of Michigan Field Hockey Team, 1987

Back Row: head coach Karen Collins, Joanne Green, Josee Charvet, Debbie Devine, Carolyn Fancher, Katrina Warner, Judy Burinskas, Gillian Pieper, ?

Middle Row: Patricia Maran, Patti Farley, Ilene Meadows, Trisha Mondul, Diane Pentaleri, Kay King,

Front Row: assistant coach Patti Smith, Sharon Cantor, Robin Ives, Sara Clark, Andrea Kuebbeler, ?