One of the potential reasons why sinuous submarine channels are uncommon on the modern seafloor at higher latitudes is the lack of large sources of significant sediment input into the deep sea. The low gradient systems with the highest-sinuosity channels (e.g., Amazon, Zaire, Indus, Bengal, Danube) are all directly linked to a large fluvial sediment source. Most of the larger rivers that drain Asia and North America into the Arctic Ocean (e.g., Kolyma, Indigirka, Lena, Yenisei, Ob) have relatively low sediment discharges \citep*{Milliman_2009}, and, under the present-day conditions with high sea level, most of the limited amount of sediment that reaches the sea never gets to the shelf edge. An exception is the Mackenzie Delta, where thick accumulations of deep-water clastic sediments are known from the subsurface (e.g., \citealp{nokey_d6435}). The analysis and arguments presented here suggest that such settings, with their high sediment supply, low gradients, and relatively long continental slopes, are favorable for the development of highly sinuous submarine channels, regardless of their latitude.
Conclusions
A new look at a number of submarine channels, using an automated workflow for calculating sinuosity and curvature, suggests that there is no robust relationship between submarine channel sinuosity and latitude. The apparent correlation between peak sinuosity and latitude for a certain set of channels \citep{Peakall_2011,Wells_2013} becomes statistically insignificant if more data points are added.
The Coriolis force is a weak force that becomes important only at large scales: assuming a flow velocity of 2 m/s, the Coriolis force exceeds the centrifugal force in the lower, channel-shaping parts of the flow only in very large channel bends, those with a radius of curvature larger than ~10,000 m. The vast majority of submarine channels on Earth do not reach these dimensions. Decreasing velocities tilt the force balance in the favor of Coriolis, even in smaller systems, and, as a result, the upper, more dilute and slower layers of turbidity currents are more likely to be affected by the Coriolis effect, even at relatively low latitudes.
Analysis of sinuosity development using a simple centerline evolution model shows that the initial low-curvature phase—during which the curvature-based Rossby number must be small—corresponds to extremely low sinuosities, and by the time there is a visible undulation in the centerline, the mean radius of curvature has dropped significantly (Fig. \ref{693028}). Channels with low but clearly visible sinuosity are likely to have established a characteristic radius of curvature early on, which is not going to significantly decrease any further.
The Coriolis-driven asymmetry in levee height is well documented in large systems located at higher latitudes. Unequal levee heights can occur in systems with high overall sinuosities, suggesting that strong Coriolis effects in the upper part of the flow can accompany a faster lower part that is dominated by centrifugal forces. This phenomenon is enhanced by differences in flow behavior: large curvatures associated with the sinuous thalweg characterize the lower part, whereas centrifugal accelerations are small in the upper part that tends not to strictly follow the underlying sinuous pattern. Channels of the Danube Fan are good examples of such systems: they are highly sinuous yet show a strong levee asymmetry. The increased levee height on the right channel banks of the Danube Channel results in preferential avulsion on the low-levee side to the left; in the long term, this leads to a characteristic large-scale channel pattern that might be possible to recognize in ancient systems.
Even in large high-latitude systems, patterns of erosion and deposition and the direction of channel migration alternate from one channel bend to the other and are consistent with an instability-driven channel evolution model. Although it is possible that the Coriolis force plays a role in limiting bend growth in a few very large systems, in the majority of submarine channels this force is unlikely to strongly affect the higher-density, faster-moving lower parts of gravity flows, which are driving the development of sinuosity.
Acknowledgements
We are grateful for discussions on submarine channel sinuosity with Zane Jobe, Alessandro Cantelli, Nick Howes, Morgan Sullivan, Tao Sun, and Jacob Covault. We are also grateful to Carmen Fraticelli for inviting us to present this work at the SEPM (Society for Sedimentary Geology) Research Conference and to Chevron Energy Technology Company for permission to publish. Reviews by Kyle Straub and Michael Sweet have greatly improved the paper.