Where and Why Do Submarine Canyons Remain Connected to the Shore During Sea‐Level Rise? Insights From Global Topographic Analysis and Bayesian Regression.

The efficiency of sediment routing from land to the ocean depends on the position of submarine canyon heads with regard to terrestrial sediment sources. We aim to identify the main controls on whether a submarine canyon head remains connected to terrestrial sediment input during Holocene sea‐level rise. Globally, we identified 798 canyon heads that are currently located at the 120m‐depth contour (the Last Glacial Maximum shoreline) and 183 canyon heads that are connected to the shore (within a distance of 6 km) during the present‐day highstand. Regional hotspots of shore‐connected canyons are the Mediterranean active margin and the Pacific coast of Central and South America. We used 34 terrestrial and marine predictor variables to predict shore‐connected canyon occurrence using Bayesian regression. Our analysis shows that steep and narrow shelves facilitate canyon‐head connectivity to the shore. Moreover, shore‐connected canyons occur preferentially along active margins characterized by resistant bedrock and high river‐water discharge. Plain Language Summary: Since the last glaciation about 20,000 years ago, sea level has risen by about 120 m. As a consequence, most coastlines have migrated landward, inundating large shelf areas. Some of these areas are now dissected by submarine canyons. However, with only 4% of the world's submarine canyons reaching today's coastline, these canyons remain the exception. Here, we aim to identify the environmental factors and processes that control whether rates of headward canyon incision can keep pace with landward migration of the coastline during the Holocene. We determine 34 variables that potentially predict whether a canyon remains connected to the coastline. We find that shore‐connected canyons preferentially occur along continental margins with narrow and steep shelves, such as the Mediterranean active margin and the Pacific coast of Central and South America. Moreover, our analysis supports the occurrence of such canyons offshore river basins, that are characterized by resistant bedrock and high water discharge. Such rivers deliver coarse‐grained sediment to submarine canyons, which can erode the canyon head and floor. To this end, our analysis offers new insights into the formation and maintenance of submarine canyons that are required to efficiently transport sediments, pollutants, and organic carbon from rivers to the ocean floor. Key Points: Presently, 183 submarine canyons are connected to the shoreline (within 6 km) along the world's major continentsNarrow shelves and high shelf gradients precondition the maintenance of canyon‐head connectivity to the shoreCanyon heads preferentially remain connected to the shore offshore river catchments with resistant bedrock and high water discharge [ABSTRACT FROM AUTHOR]