- Email: [email protected]
Bathymetry of the Arctic Ocean north of 85° N latitude—reply
291
they are undoubtedly wrong in detail and could possibly be wrong in their total approach. Sobczak, with his data points five to ten times further apart that the width of the features whose existence he attempts to refute, is in no position to make a ruling on that possibility. REFERENCES Beal, M.A., 1969. Bathymetry and Structure of the Arctic Ocean. Thesis, Oregon State University, Corvallis, Ore., 205 pp. Eardley, A.J., 1961. History of geologic thought on the origin of the Arctic Basin. In: G.O. Raasch (Editor), Geology of The Arctic, 1. University of Toronto Press, Toronto, Ont., pp. 607-621. Heezen, B.C. and Ewing, M., 1961. The mid-oceanic ridge and its extension through the Arctic Basin. In: G.O. Raasch (Editor), Geology of The Arctic. 1. University of Toronto Press, Toronto, Ont., pp. 622-642. Heezen, B.C. and Tharp, M., 1971. Arctic Ocean Floor. Map. National Geographic Society. Heezen, B.C. and Tharp, M., 1975. Map of the Arctic Region. Am. Geogr. Sot., World 1 : 5,000,000, Sheet 14. Ostenso, N.A. and Wold, R.J., 1977. A seismic and gravity profile across the Arctic Ocean Basin. Tectonophysics, 31: l-24. Sobczak, L.W., 1977. Bathymetry of the Arctic Ocean north of 85’N latitude. Tectonophysics, 42: T27-T33.
BATHYMETRY OF THE ARCTIC OCEAN NORTH OF 85”N LATITUDE - REPLY
L.W. SOBCZAK Earth Physics (Canada)
Branch,
(Received May 8,1978;
Gravity
and Geodynamics
Division,
accepted for publication Pecember
Ottawa,
KlA
OY3 Ont.
5,1978)
The purpose of my original letter (Sobczak, 1977) was to compare a portion of the bathymetric map published by Heezen and Tharp (1975) with a newly compiled and updated bathymetric chart and to point out significant differences in morphology and positioning, and not merely minor variations in contours. Figure 1 (fig. 2 from Sobczak, 1977) has been modified to take into account Monahan’s comments regarding missing and mislabelled contours, a submarine track, and a sounding location. Additional modifications have been made to Fig. 1 based on ice island T3 and British submarine Sovereign data. This modified chart (Fig. 1) is one of 22 charts (plotting scale 1 : 2,000,OOO) used to compile an Arctic Ocean bathymetric map at a scale of
QO”/E
_ 0”
sonw Fig. 1. Bathymetry north of 85’N. Contour interval is 500 m. Straight lines indicate location of nuclear submarine traverses along which water depth echograms were taken. Dots indicate spot soundings taken from the sea ice. l-6 are seamounts.
1 : 7,500,OOO (Sobczak and Sweeney, 1978). The latter has been compiled from nearly l/4 million digitized water depths, about 7 million values in analog form and several thousand values taken from plotting sheets. LOMONOSOV RIDGE
My representation of the Lomonosov Ridge in the vicinity of Ellesmere Island closely agrees with that of De Leeuw (1967) and is supported by soundings made from ice island Arlis II which drifted across the ridge at approxima~ly 87.5*N (Ostenso and Wold, 1977). There are no data to sup-
299
port Heezen and Tharp’s position of the ridge. Mr. Monahan claims the 80 km dextral offset shown along 165”W from the North Pole is hardly a major feature and in any event is not new information. I agree that earlier maps (Eardley, 1961) indicated a slight offset but it was not shown by Heezen and Tharp (1975). There are five submarine traverses and about six soundings from various sources to support my contours. Comparisons of contours on the Soviet side of Lomonosov Ridge were not made because very few soundings exist in this region. The contours are based primarily on one submarine track which generally supports the location of the ridge shown by Heezen and Tharp (1975). MARVIN
SEA MOUNTS
The sounding data confirm that there are at least six separate sea-mounts. The minimum water depths listed in table I of Sobczak (1977) are the minimum values recorded. The table does not suggest that these are the minimum water depths for each particular sea mount or imply their accuracy. This topic was discussed briefly by Sobczak et al. (1973) for Canadian bathymetric data. Methods, corrections to the data, etc. were not discussed because the intent of the paper was to comment on major differences between the two charts. The data are discussed, however, by Sobczak and Sweeney (1978). ALPHA
RIDGE
Differences between the results I have presented in Fig. 1 and those of Heezen and Tharp (1975) are easily seen by a comparison of the maps presented and I leave it to the readers discretion. It has been acknowledged (Sobczak, 1977) that the two features were grossly similar. MORRIS
JESUP PLATEAU
The plateau is not dissected by a major valley as shown by Heezen and Tharp (1975) but rather a single elongated plateau as clearly indicated by the Arlis II data (Ostenso and Wold, 1977) and the data collected by the British submarine Sovereign (G.L. Johnson, personal communication, 1977). NANSEN-GAKKEL
RIDGE
The Nansen--Gakkel Ridge as depicted by Heezen and Tharp is diagrammatic (M. Tharp, personal communication, 1977) yet Monahan still wants to defend their representation of the ridge. Figure 1 of Sobczak (1977) indicates that the position and strike of the ridge are similar to that of Heezen
300
and Tharp. However, submarine profiles across the ridge reveal a rugged topography of alternating narrow peaks and troughs with widths of about 20 km (Sobczak and Sweeney, 1978), not a topography with wide flat-top elevated areas separated by narrow troughs as shown by Heezen and Tharp (1975). Moving the traverse location does not resolve these differences. Secondly the magnetic anomaly pattern over the Greenland end of the ridge (Coles et al., 1978) does not support the large transform offsets or the location of the median valley indicated by Heezen and Tharp. Thirdly Monahan indicates that the complex relief of the Mid-Atlantic Ridge was not properly determined until the detailed sounding surveys of the nineteen-sixties, and that for reasons outlined in Heezen and Ewing (1961), Heezen and Tharpe decided that the morphology of the Nansen--Gakkel Ridge was similar to that of the Mid-Atlantic Ridge. Heezen and Ewing (1961) did not claim morphologic similarity between the two ridges but suggested that the extension of the mid-oceanic ridge continued through the Arctic Basin. Comparison of the Heezen and Tharp map with other bathymetric charts of the more thoroughly studied Mid-Atlantic Ridge is instructive (Fig. 2). In the vicinity of Jan Mayan Island, for example, Heezen and Tharp show a system of troughs (transform faults) with water depths in excess of 3000 m as opposed to water depths generally around 2000 m with a few values up to 2500 m shown on the charts by Perry et al. (1978), Gronlie and Talwani (1977), and German plotting sheets (Zichwolff, personal communication, 1976). In addition Perry et al. (1978) show a northeast elongated pattern of peaks and troughs that bear very little resemblance to the Heezen and Tharp (1975) blocky, transform fault pattern. A similar elongated pattern in this region is shown by unpublished British bathymetric charts (AS. Laughton, personal communication, 1977), and by the Gronlie and TaIwani (1977) bathymetric map. If a similarity argument is to be used to guide our judgement in drawing bathymetric contours along the Nansen-Gakkel Ridge, there is ample evidence to support the elongated pattern of the Nansen-Gakkel Ridge shown in Fig. 1. Data are sparse, however, and many revisions will be required, but the elongated pattern characteristic of the ridge is real. Heezen and Ewing (1961, p. 631), commenting on bathymetric maps published by Soviet investigators who did not show the location or the value of individual soundings, said that such contour charts are by themselves of limited use as it is impossible to distinguish fact from fiction and thus they were reluctant to accept contours without supporting evidence. The bathymetric chart shown in Fig. 1 is only one of 22 plotting sheets contoured in a manner consistent with the soundings plotted. The data distribution is shown and bathymetric contours are dashed over areas where control is poor. My philosophy towards contouring is that the contours must fit the existing data, Contrary to Monahan’s claim, a map is not an abstraction, but rather a representation and consequently one may indeed talk about the accuracy of representation. The accuracy of any map or chart is first and
a
b
Fig. 2. a. Bathymetry of the North Atlantic Ocean taken from Perry et al. (1978). Contour interval is 500 m. b. Bathymetry of the North Atlantic Ocean taken from Heezen ant Tharp (1975). Contour interval is 500 m.
302
foremost scale.
dependent
on the quality
and quantity
of the data and not on the
ACKNOWLEDGEMENTS
I am particularly grateful to Drs. K. Whitham and J.G. Tanner for their support and encour~ement, to Drs. M.D. Thomas, R.A. Gibb and J.F. Sweeney who were helpful in commenting on and editing of this reply and to Mr. L. Warren who drafted the drawings. Data were received from many sources as acknowledged in Sobczak and Sweeney (1978). REFERENCES BeaI, M.A., 1969. Bathymetry and Structure of the Arctic Ocean. Thesis, Oregon State Univ., Corvallis, Ore., 204 pp. Coles, R.L., Hannaford, W. and Haines, G.V., 1978. Magnetic anomalies and the evolution of the Arctic. In: J.F. Sweeney (Editor), Arctic Geophysical Review. PubI. Earth Phys. Branch, 45(4): 51-66. De Leeuw, M.M., 1967. New Canadian bathymetric chart of the western Arctic Ocean, north of 72’. DeepSea Res., 14: 489-504. Eardley, A.J., 1961. History of geologic thought on the origin of the Arctic Basin. In: G.O. Raasch (Editor), Geology of the Arctic, 1. University of Toronto Press, Toronto, Ont., pp. 607-621. Gronlie, G. and Talwani, M., 1977. Bathymetry of the Norwegian~ree~~d Seas (map). University of Oslo, Norway and Lamont-Doherty Geological Observatory, Palisades, N.Y. Heezen, B.C. and Ewing, M., 1961. The mid-oceanic ridge and its extension through the Arctic Basin. In: G.0. Raasch (Editor), Geology of the Arctic, 1. University of Toronto Press, Toronto, Ont., pp. 622-642. Heezen, B.C., and Tharp, M., 1971. Arctic Ocean Floor Map. National Geographic Society. Heezen, B.C., and Tharp,,M.,. 1975. Map of the Arctic Region. Am. Geogr. Sot., LamontDoherty Geological Observatory, Columbia University. Ostenso, N.A. and Weld, R-J., 1977. A seismic and gravity profile across the Arctic Ocean Basin. Tectonophysics, 37 : l-24. Ferry, R.K., Fleming, H.S., Cherkis, N.Z., Feden, R.H. and Massingill, J.V., 1978. Batymetry of the Norwegian+lreenland and western Barents Seas (map). U.S. Navai Research Laboratory, Acoustics Division, Washington, D.C. Sobczak, L.W., 1977. Bathymetry of the Arctic Ocean north of 85’N latitude. Tectonophysics, 42: T27-T33. Sobczak, L.W. and Sweeney, J.F., 1978. Bathymetry of the Arctic Ocean. In: J.F. Sweeney (Editor), Arctic Geophysical Review. Publ. Earth Phys. Branch, 45(4): 7-14. Sobczak, L-W., Stephens, L.E., Winter, P.J. and Hearty, D.B., 1973. Gravity measurements over the Beaufort Sea, Banks Island and Mackenzie Delta. Earth Phys. Branch, Gravity Map Ser., 151: 16 pp.
they are undoubtedly wrong in detail and could possibly be wrong in their total approach. Sobczak, with his data points five to ten times further apart that the width of the features whose existence he attempts to refute, is in no position to make a ruling on that possibility. REFERENCES Beal, M.A., 1969. Bathymetry and Structure of the Arctic Ocean. Thesis, Oregon State University, Corvallis, Ore., 205 pp. Eardley, A.J., 1961. History of geologic thought on the origin of the Arctic Basin. In: G.O. Raasch (Editor), Geology of The Arctic, 1. University of Toronto Press, Toronto, Ont., pp. 607-621. Heezen, B.C. and Ewing, M., 1961. The mid-oceanic ridge and its extension through the Arctic Basin. In: G.O. Raasch (Editor), Geology of The Arctic. 1. University of Toronto Press, Toronto, Ont., pp. 622-642. Heezen, B.C. and Tharp, M., 1971. Arctic Ocean Floor. Map. National Geographic Society. Heezen, B.C. and Tharp, M., 1975. Map of the Arctic Region. Am. Geogr. Sot., World 1 : 5,000,000, Sheet 14. Ostenso, N.A. and Wold, R.J., 1977. A seismic and gravity profile across the Arctic Ocean Basin. Tectonophysics, 31: l-24. Sobczak, L.W., 1977. Bathymetry of the Arctic Ocean north of 85’N latitude. Tectonophysics, 42: T27-T33.
BATHYMETRY OF THE ARCTIC OCEAN NORTH OF 85”N LATITUDE - REPLY
L.W. SOBCZAK Earth Physics (Canada)
Branch,
(Received May 8,1978;
Gravity
and Geodynamics
Division,
accepted for publication Pecember
Ottawa,
KlA
OY3 Ont.
5,1978)
The purpose of my original letter (Sobczak, 1977) was to compare a portion of the bathymetric map published by Heezen and Tharp (1975) with a newly compiled and updated bathymetric chart and to point out significant differences in morphology and positioning, and not merely minor variations in contours. Figure 1 (fig. 2 from Sobczak, 1977) has been modified to take into account Monahan’s comments regarding missing and mislabelled contours, a submarine track, and a sounding location. Additional modifications have been made to Fig. 1 based on ice island T3 and British submarine Sovereign data. This modified chart (Fig. 1) is one of 22 charts (plotting scale 1 : 2,000,OOO) used to compile an Arctic Ocean bathymetric map at a scale of
QO”/E
_ 0”
sonw Fig. 1. Bathymetry north of 85’N. Contour interval is 500 m. Straight lines indicate location of nuclear submarine traverses along which water depth echograms were taken. Dots indicate spot soundings taken from the sea ice. l-6 are seamounts.
1 : 7,500,OOO (Sobczak and Sweeney, 1978). The latter has been compiled from nearly l/4 million digitized water depths, about 7 million values in analog form and several thousand values taken from plotting sheets. LOMONOSOV RIDGE
My representation of the Lomonosov Ridge in the vicinity of Ellesmere Island closely agrees with that of De Leeuw (1967) and is supported by soundings made from ice island Arlis II which drifted across the ridge at approxima~ly 87.5*N (Ostenso and Wold, 1977). There are no data to sup-
299
port Heezen and Tharp’s position of the ridge. Mr. Monahan claims the 80 km dextral offset shown along 165”W from the North Pole is hardly a major feature and in any event is not new information. I agree that earlier maps (Eardley, 1961) indicated a slight offset but it was not shown by Heezen and Tharp (1975). There are five submarine traverses and about six soundings from various sources to support my contours. Comparisons of contours on the Soviet side of Lomonosov Ridge were not made because very few soundings exist in this region. The contours are based primarily on one submarine track which generally supports the location of the ridge shown by Heezen and Tharp (1975). MARVIN
SEA MOUNTS
The sounding data confirm that there are at least six separate sea-mounts. The minimum water depths listed in table I of Sobczak (1977) are the minimum values recorded. The table does not suggest that these are the minimum water depths for each particular sea mount or imply their accuracy. This topic was discussed briefly by Sobczak et al. (1973) for Canadian bathymetric data. Methods, corrections to the data, etc. were not discussed because the intent of the paper was to comment on major differences between the two charts. The data are discussed, however, by Sobczak and Sweeney (1978). ALPHA
RIDGE
Differences between the results I have presented in Fig. 1 and those of Heezen and Tharp (1975) are easily seen by a comparison of the maps presented and I leave it to the readers discretion. It has been acknowledged (Sobczak, 1977) that the two features were grossly similar. MORRIS
JESUP PLATEAU
The plateau is not dissected by a major valley as shown by Heezen and Tharp (1975) but rather a single elongated plateau as clearly indicated by the Arlis II data (Ostenso and Wold, 1977) and the data collected by the British submarine Sovereign (G.L. Johnson, personal communication, 1977). NANSEN-GAKKEL
RIDGE
The Nansen--Gakkel Ridge as depicted by Heezen and Tharp is diagrammatic (M. Tharp, personal communication, 1977) yet Monahan still wants to defend their representation of the ridge. Figure 1 of Sobczak (1977) indicates that the position and strike of the ridge are similar to that of Heezen
300
and Tharp. However, submarine profiles across the ridge reveal a rugged topography of alternating narrow peaks and troughs with widths of about 20 km (Sobczak and Sweeney, 1978), not a topography with wide flat-top elevated areas separated by narrow troughs as shown by Heezen and Tharp (1975). Moving the traverse location does not resolve these differences. Secondly the magnetic anomaly pattern over the Greenland end of the ridge (Coles et al., 1978) does not support the large transform offsets or the location of the median valley indicated by Heezen and Tharp. Thirdly Monahan indicates that the complex relief of the Mid-Atlantic Ridge was not properly determined until the detailed sounding surveys of the nineteen-sixties, and that for reasons outlined in Heezen and Ewing (1961), Heezen and Tharpe decided that the morphology of the Nansen--Gakkel Ridge was similar to that of the Mid-Atlantic Ridge. Heezen and Ewing (1961) did not claim morphologic similarity between the two ridges but suggested that the extension of the mid-oceanic ridge continued through the Arctic Basin. Comparison of the Heezen and Tharp map with other bathymetric charts of the more thoroughly studied Mid-Atlantic Ridge is instructive (Fig. 2). In the vicinity of Jan Mayan Island, for example, Heezen and Tharp show a system of troughs (transform faults) with water depths in excess of 3000 m as opposed to water depths generally around 2000 m with a few values up to 2500 m shown on the charts by Perry et al. (1978), Gronlie and Talwani (1977), and German plotting sheets (Zichwolff, personal communication, 1976). In addition Perry et al. (1978) show a northeast elongated pattern of peaks and troughs that bear very little resemblance to the Heezen and Tharp (1975) blocky, transform fault pattern. A similar elongated pattern in this region is shown by unpublished British bathymetric charts (AS. Laughton, personal communication, 1977), and by the Gronlie and TaIwani (1977) bathymetric map. If a similarity argument is to be used to guide our judgement in drawing bathymetric contours along the Nansen-Gakkel Ridge, there is ample evidence to support the elongated pattern of the Nansen-Gakkel Ridge shown in Fig. 1. Data are sparse, however, and many revisions will be required, but the elongated pattern characteristic of the ridge is real. Heezen and Ewing (1961, p. 631), commenting on bathymetric maps published by Soviet investigators who did not show the location or the value of individual soundings, said that such contour charts are by themselves of limited use as it is impossible to distinguish fact from fiction and thus they were reluctant to accept contours without supporting evidence. The bathymetric chart shown in Fig. 1 is only one of 22 plotting sheets contoured in a manner consistent with the soundings plotted. The data distribution is shown and bathymetric contours are dashed over areas where control is poor. My philosophy towards contouring is that the contours must fit the existing data, Contrary to Monahan’s claim, a map is not an abstraction, but rather a representation and consequently one may indeed talk about the accuracy of representation. The accuracy of any map or chart is first and
a
b
Fig. 2. a. Bathymetry of the North Atlantic Ocean taken from Perry et al. (1978). Contour interval is 500 m. b. Bathymetry of the North Atlantic Ocean taken from Heezen ant Tharp (1975). Contour interval is 500 m.
302
foremost scale.
dependent
on the quality
and quantity
of the data and not on the
ACKNOWLEDGEMENTS
I am particularly grateful to Drs. K. Whitham and J.G. Tanner for their support and encour~ement, to Drs. M.D. Thomas, R.A. Gibb and J.F. Sweeney who were helpful in commenting on and editing of this reply and to Mr. L. Warren who drafted the drawings. Data were received from many sources as acknowledged in Sobczak and Sweeney (1978). REFERENCES BeaI, M.A., 1969. Bathymetry and Structure of the Arctic Ocean. Thesis, Oregon State Univ., Corvallis, Ore., 204 pp. Coles, R.L., Hannaford, W. and Haines, G.V., 1978. Magnetic anomalies and the evolution of the Arctic. In: J.F. Sweeney (Editor), Arctic Geophysical Review. PubI. Earth Phys. Branch, 45(4): 51-66. De Leeuw, M.M., 1967. New Canadian bathymetric chart of the western Arctic Ocean, north of 72’. DeepSea Res., 14: 489-504. Eardley, A.J., 1961. History of geologic thought on the origin of the Arctic Basin. In: G.O. Raasch (Editor), Geology of the Arctic, 1. University of Toronto Press, Toronto, Ont., pp. 607-621. Gronlie, G. and Talwani, M., 1977. Bathymetry of the Norwegian~ree~~d Seas (map). University of Oslo, Norway and Lamont-Doherty Geological Observatory, Palisades, N.Y. Heezen, B.C. and Ewing, M., 1961. The mid-oceanic ridge and its extension through the Arctic Basin. In: G.0. Raasch (Editor), Geology of the Arctic, 1. University of Toronto Press, Toronto, Ont., pp. 622-642. Heezen, B.C., and Tharp, M., 1971. Arctic Ocean Floor Map. National Geographic Society. Heezen, B.C., and Tharp,,M.,. 1975. Map of the Arctic Region. Am. Geogr. Sot., LamontDoherty Geological Observatory, Columbia University. Ostenso, N.A. and Weld, R-J., 1977. A seismic and gravity profile across the Arctic Ocean Basin. Tectonophysics, 37 : l-24. Ferry, R.K., Fleming, H.S., Cherkis, N.Z., Feden, R.H. and Massingill, J.V., 1978. Batymetry of the Norwegian+lreenland and western Barents Seas (map). U.S. Navai Research Laboratory, Acoustics Division, Washington, D.C. Sobczak, L.W., 1977. Bathymetry of the Arctic Ocean north of 85’N latitude. Tectonophysics, 42: T27-T33. Sobczak, L.W. and Sweeney, J.F., 1978. Bathymetry of the Arctic Ocean. In: J.F. Sweeney (Editor), Arctic Geophysical Review. Publ. Earth Phys. Branch, 45(4): 7-14. Sobczak, L-W., Stephens, L.E., Winter, P.J. and Hearty, D.B., 1973. Gravity measurements over the Beaufort Sea, Banks Island and Mackenzie Delta. Earth Phys. Branch, Gravity Map Ser., 151: 16 pp.