PROXY INDICATORS OF THE SURFACE ATLANTIC MERIDIONAL OVERTURNING CIRCULATION STRENGTH DURING RECENT MILLENNIA: A NEED FOR PROXY/MODEL COMPARISONS (Invited Presentation)

Instrumental series of Gulf Stream/North Atlantic Current and Atlantic meridional overturning circulation (AMOC) dynamics are limited to a few decades, hence geological proxy archives are needed to elucidate the past behavior of these systems. In particular, highly resolved proxy data located within the influence of the surface AMOC are highly desirable. Several of these well-positioned proxy records, spanning the sub-tropics to the Arctic, indicate that the surface component of the AMOC was relatively robust during the Medieval Climate Anomaly (MCA) (ca. AD 900 to 1200) and gradually weakened during the Little Ice Age (LIA) (ca. AD 1350 to 1850). Yet, the fundamental reason for this change in the surface AMOC is still widely debated. The wind-driven portion of the surface AMOC may have been linked to the winter North Atlantic Oscillation (NAO) dynamics. The winter NAO index was largely positive during the MCA and transitioned to a negative/neutral mode during the LIA (Trouet et al., 2009). Further, the marine proxy data noted here are fairly consistent with a coupled NAO/AMOC response during the last 1000 years. However, a thorough proxy/modeling comparison using the winter NAO reconstruction of Trouet et al. (2009) is needed to test this hypothesis.