Editing Downwelling (section)

=== Fronts and filaments ===
[[Front (oceanography)|Ocean fronts]] are formed by the horizontal convergence of dissimilar water masses. They can develop at regions of [[Fresh water|freshwater]] input marked by horizontal density gradients due to salinity and temperature differences or the stretching and elongation of rotating flows.<ref name="Thomas-2008" /> 

Submesoscale fronts and filaments are formed by ocean current interactions and flow instabilities. They are regions that connect the surface layer and the ocean interior.<ref>{{Cite journal |last1=Mahadevan |first1=Amala |last2=Tandon |first2=Amit |date=January 2006 |title=An analysis of mechanisms for submesoscale vertical motion at ocean fronts |url=https://linkinghub.elsevier.com/retrieve/pii/S1463500306000540 |journal=Ocean Modelling |language=en |volume=14 |issue=3–4 |pages=241–256 |doi=10.1016/j.ocemod.2006.05.006|bibcode=2006OcMod..14..241M }}</ref> These regions are characterized by horizontal [[buoyancy]] gradients < 10 km in scale, caused by sloping isopycnals. Two primary mechanisms transport surface waters to depth: the [[Adiabatic process|adiabatic]] tilting and relaxation of these isopycnals, and along-isopycnal flow or subduction.<ref>{{Cite journal |last1=Freilich |first1=Mara |last2=Mahadevan |first2=Amala |date=May 2021 |title=Coherent Pathways for Subduction From the Surface Mixed Layer at Ocean Fronts |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JC017042 |journal=Journal of Geophysical Research: Oceans |language=en |volume=126 |issue=5 |doi=10.1029/2020JC017042 |bibcode=2021JGRC..12617042F |issn=2169-9275|doi-access=free |hdl=1912/27707 |hdl-access=free }}</ref> These mechanisms can transport surface properties, such as [[heat]], below the mixed layer and assist in [[carbon sequestration]] through the [[biological pump]].<ref>{{Cite journal |last1=Mahadevan |first1=Amala |last2=Pascual |first2=Ananda |last3=Rudnick |first3=Daniel L. |last4=Ruiz |first4=Simón |last5=Tintoré |first5=Joaquín |last6=D’Asaro |first6=Eric |date=2020-11-01 |title=Coherent Pathways for Vertical Transport from the Surface Ocean to Interior |url=https://journals.ametsoc.org/view/journals/bams/101/11/bamsD190305.xml |journal=Bulletin of the American Meteorological Society |volume=101 |issue=11 |pages=E1996–E2004 |doi=10.1175/BAMS-D-19-0305.1 |issn=0003-0007|doi-access=free |hdl=10261/242771 |hdl-access=free }}</ref> [[Computer simulation|Numerical models]] predict vertical velocities at submesoscale fronts on the order of 100 m/day.<ref name="Thomas-2008">{{Citation |last1=Thomas |first1=Leif N. |title=Submesoscale processes and dynamics |date=2008 |url=https://onlinelibrary.wiley.com/doi/10.1029/177GM04 |journal=Geophysical Monograph Series |volume=177 |pages=17–38 |editor-last=Hecht |editor-first=Matthew W. |access-date=2023-11-28 |place=Washington, D. C. |publisher=American Geophysical Union |language=en |doi=10.1029/177gm04 |isbn=978-0-87590-442-9 |last2=Tandon |first2=Amit |last3=Mahadevan |first3=Amala |bibcode=2008GMS...177...17T |editor2-last=Hasumi |editor2-first=Hiroyasu}}</ref> However, vertical velocities over 1000 m/day have been observed using ocean [[Float (nautical)|floats.]]<ref>{{Cite journal |last1=D’Asaro |first1=Eric A. |last2=Shcherbina |first2=Andrey Y. |last3=Klymak |first3=Jody M. |last4=Molemaker |first4=Jeroen |last5=Novelli |first5=Guillaume |last6=Guigand |first6=Cédric M. |last7=Haza |first7=Angelique C. |last8=Haus |first8=Brian K. |last9=Ryan |first9=Edward H. |last10=Jacobs |first10=Gregg A. |last11=Huntley |first11=Helga S. |last12=Laxague |first12=Nathan J. M. |last13=Chen |first13=Shuyi |last14=Judt |first14=Falko |last15=McWilliams |first15=James C. |date=2018-02-06 |title=Ocean convergence and the dispersion of flotsam |journal=Proceedings of the National Academy of Sciences |language=en |volume=115 |issue=6 |pages=1162–1167 |doi=10.1073/pnas.1718453115 |issn=0027-8424 |pmc=5819445 |pmid=29339497 |bibcode=2018PNAS..115.1162D |doi-access=free }}</ref> These observations are rare because ship-based sensors do not have sufficient accuracy to measure vertical velocities.