Interactions between the PDO, NAO, and Arctic black carbon deposition

Rapid melting of Arctic ice presents a significant positive forcing on the global climate system, highlighting the need to understand the forces determining melting rates. Black carbon (BC) deposition on Arctic snow and ice decreases surface albedo and increases surface and atmospheric warming, accelerating ice melt. BC is transported to the Arctic from the mid-latitudes. In the past, Europe was a primary winter source and Siberian biomass burning a large summertime contributor. In recent years, Asian emissions have become the largest wintertime contributor. Studies have found a relationship between the North Atlantic Oscillation (NAO) and northward BC transport, indicating more BC reaches the Arctic during the positive NAO phase. This study revisits this hypothesis and explores the role of the Pacific Decadal Oscillation (PDO) in Arctic BC deposition. New research suggests the PDO and NAO are more closely related than previously believed. To explore the relationship between PDO, NAO and Arctic BC, a transient historical (1850-2008) simulation has been generated using the CAM-Chem model. Two distinct PDO regimes, PDO+ and PDO-, were analyzed in conjunction with the NAO. Results indicate the PDO has a minor individual impact on BC, but the phase modulates the relative NAO role in BC transport and deposition. The PDO generated positive reinforcement in horizontal and vertical winds and precipitable water lead to changes in Arctic BC transport, precipitation, and wet deposition rates, and the responses demonstrate strong seasonality with winter and spring dominance. The results suggest transport pathway dependence on the relative signs of the NAO and PDO, but further study using specific tracers is necessary for confirmation.