The origin of the Amerasia Basin, in the Arctic region, is nowadays a highly controversial topic due to the paucity of geophysical data available and the difficulties in interpreting possible seafloor spreading magnetic anomalies. The Chukchi Borderland, that extends into the Amerasia Basin north of the Chukchi Sea, has proven to be one of the more difficult features of the arctic to understand in any model for the tectonic evolution of the Amerasian Basin. In the summer of 2005, USCG Icebreaker Healy crossed the Arctic Ocean from Dutch Harbor, Alaska, to Troms�, Norway, to collect geophysical data and take shallow cores in an effort to gain greater insight into the paleo-oceanographic, depositional and tectonic history of the Arctic basins. 780 km of new seismic lines from the Chukchi Borderland are presented along with a preliminary interpretation of the tectonic evolution of the Amerasia Basin in light of the new observations. The data provide high quality images of the region down to the basement and, in areas, images below the basement. The pelagic sediment cover varies along the profiles with thicknesses ranging from less than 0.1 s to a maximum of 1.5 s TWT. Significant extensional normal faults, striking approximately north-south, are observed throughout the dataset with strong evidence of growth faults below a major unconformity. Along the reflection images oriented E-W, young sediments and possibly the seafloor show small offsets. While this may be due to differential compaction or fluid expulsion, the presence of low amplitude folds above the footwalls suggests a recent fault-propagation folding process. This may indicate recent reactivation and rotation of the crustal blocks, although the total amount of displacement and strain are very small. We do not observe compressional or inversion structures anywhere in the dataset. The orientation of the structures imaged is similar to those observed along the Mendeleev Ridge to the west, which may support recent models that propose the Chukchi Borderlands and Mendeleev Ridge comprise a single extensional province that rifted from the Siberian margin.

Our understanding of the global marine xed nitrogen budget has undergone rapid growth, and as a result there is debate as to whether or not it is balanced. The Arctic plays a disproportionately large role in the sink terms of this budget. This paper works to understand the role of the Canada Basin in the nitrogen cycle. We utilize two tracers of denitri cation: N2/Ar, a dissolved gas tracer, and N*, a nutrient ratio tracer. We aim to quantify the current state of nitrogen cycling in the Canada Basin, and determine its role in the global cycle. Our paired tracer method provides support for shelf denitri cation rates while providing an estimate of ventilation in the same water mass, and provides an estimate for deep benthic denitri cation rates. We observe a disconnect between N2/Ar and N* in the Paci c Upper Halocline Layer (PUHL), wherein the excess N2/Ar we expect from N* is nearly 250% larger than the excess we observe. Our calculations suggest that an approximate steady state between benthic denitri cation and gas exchange on the Chukchi shelf maintains this disconnect. Our measurements of the PUHL support the shelf denitri cation rates reported from direct measurements, and can predict wind speeds required for ventilation within a factor of two. A 1D diffusion model of the old deep waters of the Canada Basin supports benthic denitri cation rates of 0.095-0.15 Tg N y-1. Benthic denitri cation rates determined from the model are on the low end of rates in other deep basins. Our results suggest additional measurements of these tracers in the Canada Basin and surrounding areas would help to constrain both the physical and biological processes controlling nitrogen cycling. / Graduate / 0425 / jen.l.reeve@gmail.com