Evidence may indicate recent warming of shallow slope bottom water off New Jersey shore

Thermal data from boreholes on land have been used to infer recent changes in land‐surface temperatures, since these surface temperature changes propagate downward into the Earth and leave a measurable record [e.g., Pollack and Chapman, 1993].The temperature history of bottom water offshore New Jersey has been estimated using thermal data from the upper 150 m of sediment below the seafloor, and the results are surprising.The data appear to indicate a large temperature rise, on the order of 6–10°C, followed by a temperature decrease, all during the last 50–150 years and within a restricted area. Data were collected during Ocean Drilling Program (ODP) Leg 150 (Figure 1) [ Mountain et al., 1994], with the idea that shelf and slope waters might vary in temperature on decadal to centennial timescales, and that such variations should be recorded in subseafloor sediments. Like Earth's surface on land, the seafloor acts as a low‐pass filter. High‐frequency temperature variations are filtered out in the shallowest sediments and longer‐period variations penetrate to greater depths. Given typical oceanic sediment properties, seasonal signals penetrate to depths of a few meters below the seafloor (mbsf), while centennial signals may penetrate several tens to over a hundred meters.