ABSTRACT

In contrast with the geomagnetic field during historical times, the geomagnetic field during prehistoric (paleo) times is poorly described. As a result it is difficult to know the context in which to place the historical record of the geomagnetic field including features that have changed and those that have persisted. Some researchers have considered historical times to be anomalous, but if so, how anomalous? Should we be concerned about what future changes may bring or are historical behaviors that have gained attention just part of normal background variability. With better data and data analysis approaches our understanding of the prehistoric (paleo)-geomagnetic field has improved substantially over the last decade. Scientists are beginning to define paleo-geomagnetic dynamics that happen on thousands of years. But we do not know how these changes relate to historical type variations or whether the rates of change of the geomagnetic field are consistent or uneven. This project will address this through a reconstruction of the paleo-geomagnetic record of the northern North Atlantic from ultrahigh accumulating sediments that allow paleo-geomagnetic records to be developed at sub-centennial resolution through the last 10,000 years. The northern North Atlantic is an optimal location because it is a region of extreme geomagnetic sensitivity and one where high quality paleo records with little smoothing can be obtained. The latter is important as most sedimentary records smooth over historically relevant time intervals providing little context. The investigators will scrutinize present records in detail and combine them with new ultrahigh resolution records to provide high quality records with well-constrained uncertainties. This will provide fundamental observations on paleo-geomagnetic changes from a strategic location and of a quality where the interactions between millennial and shorter changes can be evaluated, and as a result, allow the investigators to place modern changes into firmer prehistoric constraints. Additionally, this project will provide an interpretive framework to more completely understand the processes deep within Earth that drive the geomagnetic field and how the geomagnetic shield that protects us from cosmic rays and solar winds varies through time and is likely to do so again; with practical implications for telecommunications, human health, and global ecosystems. Regional stratigraphic master dating curves will be refined. This project will support postdoctoral education continuing an investment in those that we have trained to make sure our initial investment does not fail. Data will be contributed to national databases and used to supplement ongoing big data studies of the geomagnetic field with well-characterized data. Exhibits and presentations on the theme What mud can tell us about Earth's magnetic field will be developed in collaboration with the OSU Marine Geology Repository and delivered to K-12, undergraduate, and adult learner through tours and classes and through the CEOAS booth at the Corvallis Saturday Market.

The geomagnetic field is changing; the question is what sort of change is taking place. Some have speculated that a polarity reversal is imminent; others have suggested that such a change, if happening at all, is thousands of years away at the soonest. Much of the ambiguity results from a lack of paleo-context from which to place the historical geomagnetic field. Even though the paleo-record is poorly constrained relative to historical, our understanding of this record is improving and suggests that we are undergoing the latest of a series of millennial scale changes of the field that describe the Holocene, but what happens on shorter timescale analogous to the historical record is essentially unknown. The change that is happening at present is just one example, but whether this is large or small or unique or normal is not known. This project will provide observational constraints on paleo-geomagnetic change from a strategic location and of a quality where the interactions between millennial/centennial and geomagnetic changes on shorter time scales can be evaluated. As a result these observations will provide a paleo-context from which to evaluate historical geomagnetic change. To do this the team will use records from the northern North Atlantic, a location of fundamental paleomagnetic importance for three essential reasons. First, the structure of the modern geomagnetic field, changes observed historically, and paleomagnetic records all point to the northern North Atlantic as a region sensitive to changes in the geomagnetic field's morphology. Second, aggressive glacial erosion of strongly magnetic bedrock, along with a vigorous redistribution system results in paleomagnetic record of high fidelity often accumulating at high rates in both marine and terrestrial (lake) settings. Third, high carbonate production and preservation in marine environments allow for detailed radiocarbon chronologies, while numerous tephra layers enable reservoir ages to be assessed resulting in well constrained chronologies. Exceptional paleo-geomagnetic records that result are capable of uncovering many aspect of the geomagnetic field with unprecedented accuracy and resolution through the Holocene. The present set of records are enlightening; unveiling features never before seen, but are far from perfect, with notable gaps over the last few thousand years, occasional discrepancies between overlapping records (especially with relative paleointensity), and have not been adequately synthesized. Significant improvements are still possible, as concerted efforts to constrain the regions paleoclimatic record have resulted in a large number of sediment cores on and around Iceland/Greenland that retain suitable properties for high fidelity paleomagnetic records. Many of these records have already been dated and some have associated paleomagnetic data (often incompletely assessed) already in place. The investigators will take advantage of these sediment archives and data to support development of a sub-centennial resolution paleo-geomagnetic reconstructions from the northern North Atlantic that overlaps with the historical record and continues through the Holocene with enough observations to constrain and reduce uncertainties in both chronology and paleomagnetic measurables. This paleo-geomagnetic synthesis will provide an interpretive framework to more completely assess past variations required to further our understanding of the geodynamo process controlling the geomagnetic field and the geomagnetic shield and its control on the production of cosmic nuclides; a hinge point for our understanding of processes ranging from solar variability to climate with practical implications for telecommunications, human health, and global ecosystems. Regional stratigraphic master dating curves will be refined. Data will be contributed to national databases (MagIC, NOAA ) providing well constrained data for ongoing spherical harmonic analyses of the geomagnetic field. Exhibits and presentations on the theme "What mud can tell us about Earth's magnetic field" will be developed in collaboration with the OSU Marine Geology Repository and delivered to K-12, undergraduate, and adult learner through tours and classes and through the CEOAS booth at the Corvallis Saturday Market.

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