What is the strength of the Earth's magnetic field at McMurdo Station, Antarctica?
According to the current World Magnetic Model 2015 v2 (new one to be released on 10 December 2019!), 

Longitude: 166.6863° E
Latitude: 77.8419° S
Elevation: 10 m

Date: 2019-11-25
Declination (+E | -W):   141.5232°    (-0.1829°/yr)
Inclination (+D | -U):   -80.3929°    (0.0399°/yr)
Horizontal Intensity:     10,396.8 nT (34.7 nT/yr)
North Comp (+N | -S):     -8,139.2 nT (-6.5 nT/yr)
East Comp (+E | -W):       6,468.8 nT (47.6 nT/yr)
Vertical Comp (+D | -U): -61,423.3 nT (54.8 nT/yr)
Total Field:              62,297.0 nT (-48.3 nT/yr)

Uncertainties:  0.57°   0.22°   133 nT  138 nT  89 nT   165 nT  152 nT