Heat flow highs on the Norwegian‐Barents‐Svalbard continental slope: Deep crustal fractures, dewatering, or “memory in the mud”?

Abstract

Heat flow transects across the Norwegian‐Barents‐Svalbard continental margin (Sundvor and Eldholm, 1992) reveal anomalously high (by about 60 mK/m) sub‐seafloor thermal gradients on the upper continental slope, at water depths about 600m–800m. Of several hypotheses which might explain these enhanced gradients, deep crustal fractures or igneous activity along the ocean continental crustal boundary (COB) is rejected by the lack of associated seismicity, extrusive/intrusive activity, or systematic correlation of gradient anomaly with the COB, which does not correspond to any specific water depth. A “Memory in the Mud” explanation is possible if the base of the Norwegian‐Atlantic (warm) current rose by ca. 150–200 m ca. 50–300 years ago. However, high local spatial variability in observed gradients renders this mechanism suspect. Alternatively the thermal gradients were locally steepened by enhanced rise of pore fluids, mud and/or methane gas. This is most likely on the upper continental slope because post‐opening sediment accumulations (i.e., dewatering) tend to be maximal there.