Temperature/salinity interleaving is a signature of thermohaline transition in the Arctic Ocean. These interleaving features, or "intrusions," are observed to decrease in amplitude as they spread laterally from warmer toward cooler water. Here this phenomenon is investigated by considering the effect of a nonlinear equation of state on intrusion structure and behavior. The analysis shows that large-scale gradients of the thermal expansion coefficient (α) can induce a spatial decay of intrusion temperature, salinity, and velocity amplitudes toward cooler water. Spatial decay implies a recirculating flow between adjacent layers, which induces a slow vertical propagation of the intrusions. The temperature-dependence of α provides a mechanism which may act to trap intrusions in the vicinity of warm Arctic boundary currents, inhibiting ventilation of cooler waters.