Extreme climatic conditions recorded in Santa Barbara Basin laminated sediments: the 1835–1840 Macoma event

Abstract

The Santa Barbara Basin (SBB) record of laminated sediment, well known for its excellent time resolution, shows the presence of an unusual once-in-a-millenium event, in the period 1835–1840, at a depth of 55–57 cm below the surface of the seafloor. This “ Macoma Event” is the brief flourishing of a macrofaunal community in the deep center of the SBB, from which large organisms are normally excluded by the lack of oxygen. Shells of the pelecypod Macoma leptonoidea Dall and associated fossils, which congregate in a thin layer dated at 1840, provide evidence for a sudden local extinction of macrobenthos by suffocation. Various stratigraphic evidence suggests that M. leptonoidea colonized the basin floor for a few years prior to 1840 as a result of temporarily decreased productivity and increased oxygen content in the water spilling over the sill into the basin. Historical eyewitness reports indicate unusually severe winter storms from southeasterly directions during the 1830s in the SBB. We suggest that coastal upwelling was severely reduced during 1835–1839 with the effect of reducing the intensity of the oxygen minimum layer. The Macoma Event apparently is one manifestation of large-scale climatic anomalies felt throughout North America, and which were possibly linked to the major volcanic eruption of Cosiguina, Nicaragua, in 1835.